diff --git a/activation/e2e/checkpoint_merged_test.go b/activation/e2e/checkpoint_merged_test.go
index cc5cfb00bd..3984d926f8 100644
--- a/activation/e2e/checkpoint_merged_test.go
+++ b/activation/e2e/checkpoint_merged_test.go
@@ -273,6 +273,12 @@ func Test_CheckpointAfterMerge(t *testing.T) {
 		require.Equal(t, i, marriage.Index)
 	}
 
+	checkpointedMerged, err := atxs.Get(newDB, mergedATX.ID())
+	require.NoError(t, err)
+	require.True(t, checkpointedMerged.Golden())
+	require.NotNil(t, checkpointedMerged.MarriageATX)
+	require.Equal(t, marriageATX.ID(), *checkpointedMerged.MarriageATX)
+
 	// 4. Spawn new ATX handler and builder using the new DB
 	poetDb = activation.NewPoetDb(newDB, logger.Named("poetDb"))
 	cdb = datastore.NewCachedDB(newDB, logger)
diff --git a/activation/handler_v2.go b/activation/handler_v2.go
index f969595dee..d68bfff844 100644
--- a/activation/handler_v2.go
+++ b/activation/handler_v2.go
@@ -118,6 +118,7 @@ func (h *HandlerV2) processATX(
 
 	atx := &types.ActivationTx{
 		PublishEpoch:   watx.PublishEpoch,
+		MarriageATX:    watx.MarriageATX,
 		Coinbase:       watx.Coinbase,
 		BaseTickHeight: baseTickHeight,
 		NumUnits:       parts.effectiveUnits,
@@ -661,6 +662,7 @@ func (h *HandlerV2) checkMalicious(
 	tx *sql.Tx,
 	watx *wire.ActivationTxV2,
 	marrying []marriage,
+	ids []types.NodeID,
 ) error {
 	malicious, err := identities.IsMalicious(tx, watx.SmesherID)
 	if err != nil {
@@ -678,6 +680,22 @@ func (h *HandlerV2) checkMalicious(
 		return nil
 	}
 
+	malicious, err = h.checkDoublePost(ctx, tx, watx, ids)
+	if err != nil {
+		return fmt.Errorf("checking double post: %w", err)
+	}
+	if malicious {
+		return nil
+	}
+
+	malicious, err = h.checkDoubleMerge(ctx, tx, watx)
+	if err != nil {
+		return fmt.Errorf("checking double merge: %w", err)
+	}
+	if malicious {
+		return nil
+	}
+
 	// TODO(mafa): contextual validation:
 	// 1. check double-publish = ID contributed post to two ATXs in the same epoch
 	// 2. check previous ATX
@@ -722,6 +740,66 @@ func (h *HandlerV2) checkDoubleMarry(
 	return false, nil
 }
 
+func (h *HandlerV2) checkDoublePost(
+	ctx context.Context,
+	tx *sql.Tx,
+	atx *wire.ActivationTxV2,
+	ids []types.NodeID,
+) (bool, error) {
+	for _, id := range ids {
+		atxids, err := atxs.FindDoublePublish(tx, id, atx.PublishEpoch)
+		switch {
+		case errors.Is(err, sql.ErrNotFound):
+			continue
+		case err != nil:
+			return false, fmt.Errorf("searching for double publish: %w", err)
+		}
+		otherAtxId := slices.IndexFunc(atxids, func(other types.ATXID) bool { return other != atx.ID() })
+		otherAtx := atxids[otherAtxId]
+		h.logger.Debug(
+			"found ID that has already contributed its PoST in this epoch",
+			zap.Stringer("node_id", id),
+			zap.Stringer("atx_id", atx.ID()),
+			zap.Stringer("other_atx_id", otherAtx),
+			zap.Uint32("epoch", atx.PublishEpoch.Uint32()),
+		)
+		// TODO(mafa): finish proof
+		proof := &wire.ATXProof{
+			ProofType: wire.DoublePublish,
+		}
+		return true, h.malPublisher.Publish(ctx, id, proof)
+	}
+	return false, nil
+}
+
+func (h *HandlerV2) checkDoubleMerge(ctx context.Context, tx *sql.Tx, watx *wire.ActivationTxV2) (bool, error) {
+	if watx.MarriageATX == nil {
+		return false, nil
+	}
+	ids, err := atxs.MergeConflict(tx, *watx.MarriageATX, watx.PublishEpoch)
+	switch {
+	case errors.Is(err, sql.ErrNotFound):
+		return false, nil
+	case err != nil:
+		return false, fmt.Errorf("searching for ATXs with the same marriage ATX: %w", err)
+	}
+	otherIndex := slices.IndexFunc(ids, func(id types.ATXID) bool { return id != watx.ID() })
+	other := ids[otherIndex]
+
+	h.logger.Debug("second merged ATX for single marriage - creating malfeasance proof",
+		zap.Stringer("marriage_atx", *watx.MarriageATX),
+		zap.Stringer("atx", watx.ID()),
+		zap.Stringer("other_atx", other),
+		zap.Stringer("smesher_id", watx.SmesherID),
+	)
+
+	// TODO(mafa): finish proof
+	proof := &wire.ATXProof{
+		ProofType: wire.DoubleMerge,
+	}
+	return true, h.malPublisher.Publish(ctx, watx.SmesherID, proof)
+}
+
 // Store an ATX in the DB.
 func (h *HandlerV2) storeAtx(
 	ctx context.Context,
@@ -769,7 +847,7 @@ func (h *HandlerV2) storeAtx(
 		// TODO(mafa): don't store own ATX if it would mark the node as malicious
 		//    this probably needs to be done by validating and storing own ATXs eagerly and skipping validation in
 		//    the gossip handler (not sync!)
-		err := h.checkMalicious(ctx, tx, watx, marrying)
+		err := h.checkMalicious(ctx, tx, watx, marrying, maps.Keys(units))
 		if err != nil {
 			return fmt.Errorf("check malicious: %w", err)
 		}
diff --git a/activation/handler_v2_test.go b/activation/handler_v2_test.go
index 21ff806037..62ff24377a 100644
--- a/activation/handler_v2_test.go
+++ b/activation/handler_v2_test.go
@@ -615,18 +615,16 @@ func TestHandlerV2_ProcessSoloATX(t *testing.T) {
 func marryIDs(
 	t testing.TB,
 	atxHandler *v2TestHandler,
-	sig *signing.EdSigner,
+	signers []*signing.EdSigner,
 	golden types.ATXID,
-	num int,
 ) (marriage *wire.ActivationTxV2, other []*wire.ActivationTxV2) {
+	sig := signers[0]
 	mATX := newInitialATXv2(t, golden)
 	mATX.Marriages = []wire.MarriageCertificate{{
 		Signature: sig.Sign(signing.MARRIAGE, sig.NodeID().Bytes()),
 	}}
 
-	for range num {
-		signer, err := signing.NewEdSigner()
-		require.NoError(t, err)
+	for _, signer := range signers[1:] {
 		atx := atxHandler.createAndProcessInitial(t, signer)
 		other = append(other, atx)
 		mATX.Marriages = append(mATX.Marriages, wire.MarriageCertificate{
@@ -645,20 +643,27 @@ func marryIDs(
 
 func TestHandlerV2_ProcessMergedATX(t *testing.T) {
 	t.Parallel()
-	golden := types.RandomATXID()
-	sig, err := signing.NewEdSigner()
-	require.NoError(t, err)
+	var (
+		golden          = types.RandomATXID()
+		signers         []*signing.EdSigner
+		equivocationSet []types.NodeID
+	)
+	for range 4 {
+		sig, err := signing.NewEdSigner()
+		require.NoError(t, err)
+		signers = append(signers, sig)
+		equivocationSet = append(equivocationSet, sig.NodeID())
+	}
+	sig := signers[0]
 
 	t.Run("happy case", func(t *testing.T) {
 		atxHandler := newV2TestHandler(t, golden)
 
 		// Marry IDs
-		mATX, otherATXs := marryIDs(t, atxHandler, sig, golden, 2)
+		mATX, otherATXs := marryIDs(t, atxHandler, signers, golden)
 		previousATXs := []types.ATXID{mATX.ID()}
-		equivocationSet := []types.NodeID{sig.NodeID()}
 		for _, atx := range otherATXs {
 			previousATXs = append(previousATXs, atx.ID())
-			equivocationSet = append(equivocationSet, atx.SmesherID)
 		}
 
 		// Process a merged ATX
@@ -695,12 +700,10 @@ func TestHandlerV2_ProcessMergedATX(t *testing.T) {
 		atxHandler.tickSize = tickSize
 
 		// Marry IDs
-		mATX, otherATXs := marryIDs(t, atxHandler, sig, golden, 4)
+		mATX, otherATXs := marryIDs(t, atxHandler, signers, golden)
 		previousATXs := []types.ATXID{mATX.ID()}
-		equivocationSet := []types.NodeID{sig.NodeID()}
 		for _, atx := range otherATXs {
 			previousATXs = append(previousATXs, atx.ID())
-			equivocationSet = append(equivocationSet, atx.SmesherID)
 		}
 
 		// Process a merged ATX
@@ -766,12 +769,10 @@ func TestHandlerV2_ProcessMergedATX(t *testing.T) {
 		atxHandler := newV2TestHandler(t, golden)
 
 		// Marry IDs
-		mATX, otherATXs := marryIDs(t, atxHandler, sig, golden, 2)
+		mATX, otherATXs := marryIDs(t, atxHandler, signers, golden)
 		previousATXs := []types.ATXID{}
-		equivocationSet := []types.NodeID{sig.NodeID()}
 		for _, atx := range otherATXs {
 			previousATXs = append(previousATXs, atx.ID())
-			equivocationSet = append(equivocationSet, atx.SmesherID)
 		}
 
 		// Process a merged ATX
@@ -803,12 +804,10 @@ func TestHandlerV2_ProcessMergedATX(t *testing.T) {
 		atxHandler := newV2TestHandler(t, golden)
 
 		// Marry IDs
-		mATX, otherATXs := marryIDs(t, atxHandler, sig, golden, 1)
+		mATX, otherATXs := marryIDs(t, atxHandler, signers[:2], golden)
 		previousATXs := []types.ATXID{mATX.ID()}
-		equivocationSet := []types.NodeID{sig.NodeID()}
 		for _, atx := range otherATXs {
 			previousATXs = append(previousATXs, atx.ID())
-			equivocationSet = append(equivocationSet, atx.SmesherID)
 		}
 
 		// Process a merged ATX
@@ -837,12 +836,10 @@ func TestHandlerV2_ProcessMergedATX(t *testing.T) {
 		atxHandler := newV2TestHandler(t, golden)
 
 		// Marry IDs
-		mATX, otherATXs := marryIDs(t, atxHandler, sig, golden, 1)
+		mATX, otherATXs := marryIDs(t, atxHandler, signers[:2], golden)
 		previousATXs := []types.ATXID{mATX.ID()}
-		equivocationSet := []types.NodeID{sig.NodeID()}
 		for _, atx := range otherATXs {
 			previousATXs = append(previousATXs, atx.ID())
-			equivocationSet = append(equivocationSet, atx.SmesherID)
 		}
 
 		// Process a merged ATX
@@ -869,11 +866,7 @@ func TestHandlerV2_ProcessMergedATX(t *testing.T) {
 		atxHandler := newV2TestHandler(t, golden)
 
 		// Marry IDs
-		mATX, otherATXs := marryIDs(t, atxHandler, sig, golden, 1)
-		equivocationSet := []types.NodeID{sig.NodeID()}
-		for _, atx := range otherATXs {
-			equivocationSet = append(equivocationSet, atx.SmesherID)
-		}
+		mATX, _ := marryIDs(t, atxHandler, signers, golden)
 
 		prev := atxs.CheckpointAtx{
 			Epoch:         mATX.PublishEpoch + 1,
@@ -933,6 +926,97 @@ func TestHandlerV2_ProcessMergedATX(t *testing.T) {
 		err = atxHandler.processATX(context.Background(), "", merged, time.Now())
 		require.ErrorIs(t, err, pubsub.ErrValidationReject)
 	})
+	t.Run("publishing two merged ATXs from one marriage set is malfeasance", func(t *testing.T) {
+		atxHandler := newV2TestHandler(t, golden)
+
+		// Marry 4 IDs
+		mATX, otherATXs := marryIDs(t, atxHandler, signers, golden)
+		previousATXs := []types.ATXID{mATX.ID()}
+		for _, atx := range otherATXs {
+			previousATXs = append(previousATXs, atx.ID())
+		}
+
+		// Process a merged ATX for 2 IDs
+		merged := newSoloATXv2(t, mATX.PublishEpoch+2, mATX.ID(), mATX.ID())
+		merged.NiPosts[0].Posts = []wire.SubPostV2{}
+		for i := range equivocationSet[:2] {
+			post := wire.SubPostV2{
+				MarriageIndex: uint32(i),
+				PrevATXIndex:  uint32(i),
+				NumUnits:      4,
+			}
+			merged.NiPosts[0].Posts = append(merged.NiPosts[0].Posts, post)
+		}
+
+		mATXID := mATX.ID()
+
+		merged.MarriageATX = &mATXID
+		merged.PreviousATXs = []types.ATXID{mATX.ID(), otherATXs[0].ID()}
+		merged.Sign(sig)
+
+		atxHandler.expectMergedAtxV2(merged, equivocationSet, []uint64{100})
+		err := atxHandler.processATX(context.Background(), "", merged, time.Now())
+		require.NoError(t, err)
+
+		// Process a second merged ATX for the same equivocation set, but different IDs
+		merged = newSoloATXv2(t, mATX.PublishEpoch+2, mATX.ID(), mATX.ID())
+		merged.NiPosts[0].Posts = []wire.SubPostV2{}
+		for i := range equivocationSet[:2] {
+			post := wire.SubPostV2{
+				MarriageIndex: uint32(i + 2),
+				PrevATXIndex:  uint32(i),
+				NumUnits:      4,
+			}
+			merged.NiPosts[0].Posts = append(merged.NiPosts[0].Posts, post)
+		}
+
+		mATXID = mATX.ID()
+		merged.MarriageATX = &mATXID
+		merged.PreviousATXs = []types.ATXID{otherATXs[1].ID(), otherATXs[2].ID()}
+		merged.Sign(signers[2])
+
+		atxHandler.expectMergedAtxV2(merged, equivocationSet, []uint64{100})
+		atxHandler.mMalPublish.EXPECT().Publish(gomock.Any(), merged.SmesherID, gomock.Any())
+		err = atxHandler.processATX(context.Background(), "", merged, time.Now())
+		require.NoError(t, err)
+	})
+	t.Run("publishing two merged ATXs (one checkpointed)", func(t *testing.T) {
+		atxHandler := newV2TestHandler(t, golden)
+
+		mATX, otherATXs := marryIDs(t, atxHandler, signers, golden)
+		mATXID := mATX.ID()
+
+		// Insert checkpointed merged ATX
+		checkpointedATX := &atxs.CheckpointAtx{
+			Epoch:       mATX.PublishEpoch + 2,
+			ID:          types.RandomATXID(),
+			SmesherID:   signers[0].NodeID(),
+			MarriageATX: &mATXID,
+		}
+		require.NoError(t, atxs.AddCheckpointed(atxHandler.cdb, checkpointedATX))
+
+		// create and process another merged ATX
+		merged := newSoloATXv2(t, checkpointedATX.Epoch, mATX.ID(), golden)
+		merged.NiPosts[0].Posts = []wire.SubPostV2{}
+		for i := range equivocationSet[2:] {
+			post := wire.SubPostV2{
+				MarriageIndex: uint32(i + 2),
+				PrevATXIndex:  uint32(i),
+				NumUnits:      4,
+			}
+			merged.NiPosts[0].Posts = append(merged.NiPosts[0].Posts, post)
+		}
+
+		merged.MarriageATX = &mATXID
+		merged.PreviousATXs = []types.ATXID{otherATXs[1].ID(), otherATXs[2].ID()}
+		merged.Sign(signers[2])
+		atxHandler.expectMergedAtxV2(merged, equivocationSet, []uint64{100})
+		// TODO: this could be syntactically validated as all nodes in the network
+		// should already have the checkpointed merged ATX.
+		atxHandler.mMalPublish.EXPECT().Publish(gomock.Any(), merged.SmesherID, gomock.Any())
+		err := atxHandler.processATX(context.Background(), "", merged, time.Now())
+		require.NoError(t, err)
+	})
 }
 
 func TestCollectDeps_AtxV2(t *testing.T) {
@@ -1732,6 +1816,64 @@ func Test_MarryingMalicious(t *testing.T) {
 	}
 }
 
+func TestContextualValidation_DoublePost(t *testing.T) {
+	t.Parallel()
+	golden := types.RandomATXID()
+	sig, err := signing.NewEdSigner()
+	require.NoError(t, err)
+
+	atxHandler := newV2TestHandler(t, golden)
+
+	// marry
+	otherSig, err := signing.NewEdSigner()
+	require.NoError(t, err)
+	othersAtx := atxHandler.createAndProcessInitial(t, otherSig)
+
+	mATX := newInitialATXv2(t, golden)
+	mATX.Marriages = []wire.MarriageCertificate{
+		{
+			Signature: sig.Sign(signing.MARRIAGE, sig.NodeID().Bytes()),
+		},
+		{
+			ReferenceAtx: othersAtx.ID(),
+			Signature:    otherSig.Sign(signing.MARRIAGE, sig.NodeID().Bytes()),
+		},
+	}
+	mATX.Sign(sig)
+
+	atxHandler.expectInitialAtxV2(mATX)
+	err = atxHandler.processATX(context.Background(), "", mATX, time.Now())
+	require.NoError(t, err)
+
+	// publish merged
+	merged := newSoloATXv2(t, mATX.PublishEpoch+2, mATX.ID(), mATX.ID())
+	post := wire.SubPostV2{
+		MarriageIndex: 1,
+		NumUnits:      othersAtx.TotalNumUnits(),
+		PrevATXIndex:  1,
+	}
+	merged.NiPosts[0].Posts = append(merged.NiPosts[0].Posts, post)
+
+	mATXID := mATX.ID()
+	merged.MarriageATX = &mATXID
+
+	merged.PreviousATXs = []types.ATXID{mATX.ID(), othersAtx.ID()}
+	merged.Sign(sig)
+
+	atxHandler.expectMergedAtxV2(merged, []types.NodeID{sig.NodeID(), otherSig.NodeID()}, []uint64{poetLeaves})
+	err = atxHandler.processATX(context.Background(), "", merged, time.Now())
+	require.NoError(t, err)
+
+	// The otherSig tries to publish alone in the same epoch.
+	// This is malfeasance as it tries include his PoST twice.
+	doubled := newSoloATXv2(t, merged.PublishEpoch, othersAtx.ID(), othersAtx.ID())
+	doubled.Sign(otherSig)
+	atxHandler.expectAtxV2(doubled)
+	atxHandler.mMalPublish.EXPECT().Publish(gomock.Any(), otherSig.NodeID(), gomock.Any())
+	err = atxHandler.processATX(context.Background(), "", doubled, time.Now())
+	require.NoError(t, err)
+}
+
 func Test_CalculatingUnits(t *testing.T) {
 	t.Parallel()
 	t.Run("units on 1 nipost must not overflow", func(t *testing.T) {
diff --git a/activation/wire/malfeasance.go b/activation/wire/malfeasance.go
index 14da4bab87..cf1a1f926d 100644
--- a/activation/wire/malfeasance.go
+++ b/activation/wire/malfeasance.go
@@ -43,6 +43,7 @@ type ProofType byte
 const (
 	DoublePublish ProofType = iota + 1
 	DoubleMarry
+	DoubleMerge
 	InvalidPost
 )
 
diff --git a/api/grpcserver/v2alpha1/network.go b/api/grpcserver/v2alpha1/network.go
index 60d4ad29ce..f9454394cc 100644
--- a/api/grpcserver/v2alpha1/network.go
+++ b/api/grpcserver/v2alpha1/network.go
@@ -11,17 +11,19 @@ import (
 	"google.golang.org/protobuf/types/known/timestamppb"
 
 	"github.com/spacemeshos/go-spacemesh/common/types"
+	"github.com/spacemeshos/go-spacemesh/config"
 )
 
 const (
 	Network = "network_v2alpha1"
 )
 
-func NewNetworkService(genesisTime time.Time, genesisID types.Hash20, layerDuration time.Duration) *NetworkService {
+func NewNetworkService(genesisTime time.Time, config *config.Config) *NetworkService {
 	return &NetworkService{
 		genesisTime:   genesisTime,
-		genesisID:     genesisID,
-		layerDuration: layerDuration,
+		genesisID:     config.Genesis.GenesisID(),
+		layerDuration: config.LayerDuration,
+		labelsPerUnit: config.POST.LabelsPerUnit,
 	}
 }
 
@@ -29,6 +31,7 @@ type NetworkService struct {
 	genesisTime   time.Time
 	genesisID     types.Hash20
 	layerDuration time.Duration
+	labelsPerUnit uint64
 }
 
 func (s *NetworkService) RegisterService(server *grpc.Server) {
@@ -54,5 +57,6 @@ func (s *NetworkService) Info(context.Context,
 		Hrp:                   types.NetworkHRP(),
 		EffectiveGenesisLayer: types.GetEffectiveGenesis().Uint32(),
 		LayersPerEpoch:        types.GetLayersPerEpoch(),
+		LabelsPerUnit:         s.labelsPerUnit,
 	}, nil
 }
diff --git a/api/grpcserver/v2alpha1/network_test.go b/api/grpcserver/v2alpha1/network_test.go
index 989ab92a1e..0e87e3a7d1 100644
--- a/api/grpcserver/v2alpha1/network_test.go
+++ b/api/grpcserver/v2alpha1/network_test.go
@@ -9,13 +9,15 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/spacemeshos/go-spacemesh/common/types"
+	"github.com/spacemeshos/go-spacemesh/config"
 )
 
 func TestNetworkService_Info(t *testing.T) {
 	ctx := context.Background()
 	genesis := time.Unix(genTimeUnix, 0)
+	c := config.DefaultTestConfig()
 
-	svc := NewNetworkService(genesis, genesisID, layerDuration)
+	svc := NewNetworkService(genesis, &c)
 	cfg, cleanup := launchServer(t, svc)
 	t.Cleanup(cleanup)
 
@@ -27,10 +29,11 @@ func TestNetworkService_Info(t *testing.T) {
 		require.NoError(t, err)
 
 		require.Equal(t, genesis.UTC(), info.GenesisTime.AsTime().UTC())
-		require.Equal(t, layerDuration, info.LayerDuration.AsDuration())
-		require.Equal(t, genesisID.Bytes(), info.GenesisId)
+		require.Equal(t, c.LayerDuration, info.LayerDuration.AsDuration())
+		require.Equal(t, c.Genesis.GenesisID().Bytes(), info.GenesisId)
 		require.Equal(t, types.NetworkHRP(), info.Hrp)
 		require.Equal(t, types.GetEffectiveGenesis().Uint32(), info.EffectiveGenesisLayer)
 		require.Equal(t, types.GetLayersPerEpoch(), info.LayersPerEpoch)
+		require.Equal(t, c.POST.LabelsPerUnit, info.LabelsPerUnit)
 	})
 }
diff --git a/api/grpcserver/v2alpha1/v2alpha1_test.go b/api/grpcserver/v2alpha1/v2alpha1_test.go
index 27d5d9f7ac..52ba08f556 100644
--- a/api/grpcserver/v2alpha1/v2alpha1_test.go
+++ b/api/grpcserver/v2alpha1/v2alpha1_test.go
@@ -11,7 +11,6 @@ import (
 	"google.golang.org/grpc/credentials/insecure"
 
 	"github.com/spacemeshos/go-spacemesh/api/grpcserver"
-	"github.com/spacemeshos/go-spacemesh/common/types"
 )
 
 const (
@@ -19,8 +18,6 @@ const (
 	layerDuration = 10 * time.Second
 )
 
-var genesisID = types.Hash20{}
-
 func launchServer(tb testing.TB, services ...grpcserver.ServiceAPI) (grpcserver.Config, func()) {
 	cfg := grpcserver.DefaultTestConfig()
 	grpc, err := grpcserver.NewWithServices(cfg.PublicListener, zaptest.NewLogger(tb).Named("grpc"), cfg, services)
diff --git a/bootstrap/updater.go b/bootstrap/updater.go
index 04f53cbdd2..9641aefb96 100644
--- a/bootstrap/updater.go
+++ b/bootstrap/updater.go
@@ -29,6 +29,7 @@ import (
 
 	"github.com/santhosh-tekuri/jsonschema/v5"
 	"github.com/spf13/afero"
+	"go.uber.org/zap"
 	"golang.org/x/sync/errgroup"
 
 	"github.com/spacemeshos/go-spacemesh/common/types"
@@ -71,7 +72,7 @@ func DefaultConfig() Config {
 
 type Updater struct {
 	cfg    Config
-	logger log.Log
+	logger *zap.Logger
 	clock  layerClock
 	fs     afero.Fs
 	client *http.Client
@@ -92,7 +93,7 @@ func WithConfig(cfg Config) Opt {
 	}
 }
 
-func WithLogger(logger log.Log) Opt {
+func WithLogger(logger *zap.Logger) Opt {
 	return func(u *Updater) {
 		u.logger = logger
 	}
@@ -113,7 +114,7 @@ func WithHttpClient(c *http.Client) Opt {
 func New(clock layerClock, opts ...Opt) *Updater {
 	u := &Updater{
 		cfg:     DefaultConfig(),
-		logger:  log.NewNop(),
+		logger:  zap.NewNop(),
 		clock:   clock,
 		fs:      afero.NewOsFs(),
 		client:  &http.Client{},
@@ -149,7 +150,7 @@ func (u *Updater) Load(ctx context.Context) error {
 		if err = u.updateAndNotify(ctx, verified); err != nil {
 			return err
 		}
-		u.logger.With().Info("loaded bootstrap file", log.Inline(verified))
+		u.logger.Info("loaded bootstrap file", zap.Inline(verified))
 		u.addUpdate(verified.Data.Epoch, verified.Persisted[len(verified.Persisted)-suffixLen:])
 	}
 	return nil
@@ -165,14 +166,14 @@ func (u *Updater) Start() error {
 			if err := u.Load(ctx); err != nil {
 				return err
 			}
-			u.logger.With().Info("start listening to update",
-				log.String("source", u.cfg.URL),
-				log.Duration("interval", u.cfg.Interval),
+			u.logger.Info("start listening to update",
+				zap.String("source", u.cfg.URL),
+				zap.Duration("interval", u.cfg.Interval),
 			)
 			for {
 				if err := u.DoIt(ctx); err != nil {
 					updateFailureCount.Add(1)
-					u.logger.With().Debug("failed to get bootstrap update", log.Err(err))
+					u.logger.Debug("failed to get bootstrap update", zap.Error(err))
 				}
 				select {
 				case <-u.stop:
@@ -233,10 +234,10 @@ func (u *Updater) DoIt(ctx context.Context) error {
 	current := u.clock.CurrentLayer().GetEpoch()
 	defer func() {
 		if err := u.prune(current); err != nil {
-			u.logger.With().Error("failed to prune",
-				log.Context(ctx),
-				log.Uint32("current epoch", current.Uint32()),
-				log.Err(err),
+			u.logger.Error("failed to prune",
+				log.ZContext(ctx),
+				zap.Uint32("current epoch", current.Uint32()),
+				zap.Error(err),
 			)
 		}
 	}()
@@ -291,7 +292,7 @@ func (u *Updater) checkEpochUpdate(
 		return nil, false, fmt.Errorf("persist bootstrap %s: %w", filename, err)
 	}
 	verified.Persisted = filename
-	u.logger.WithContext(ctx).With().Info("new bootstrap file", log.Inline(verified))
+	u.logger.Info("new bootstrap file", log.ZContext(ctx), zap.Inline(verified))
 	if err = u.updateAndNotify(ctx, verified); err != nil {
 		return verified, false, err
 	}
diff --git a/bootstrap/updater_test.go b/bootstrap/updater_test.go
index 2cc98e4c4d..4a3b712b36 100644
--- a/bootstrap/updater_test.go
+++ b/bootstrap/updater_test.go
@@ -15,11 +15,11 @@ import (
 	"github.com/spf13/afero"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/mock/gomock"
+	"go.uber.org/zap/zaptest"
 	"golang.org/x/sync/errgroup"
 
 	"github.com/spacemeshos/go-spacemesh/bootstrap"
 	"github.com/spacemeshos/go-spacemesh/common/types"
-	"github.com/spacemeshos/go-spacemesh/log/logtest"
 )
 
 const (
@@ -196,7 +196,7 @@ func TestLoad(t *testing.T) {
 			updater := bootstrap.New(
 				mc,
 				bootstrap.WithConfig(cfg),
-				bootstrap.WithLogger(logtest.New(t)),
+				bootstrap.WithLogger(zaptest.NewLogger(t)),
 				bootstrap.WithFilesystem(fs),
 			)
 			ch, err := updater.Subscribe()
@@ -248,7 +248,7 @@ func TestLoadedNotDownloadedAgain(t *testing.T) {
 	updater := bootstrap.New(
 		mc,
 		bootstrap.WithConfig(cfg),
-		bootstrap.WithLogger(logtest.New(t)),
+		bootstrap.WithLogger(zaptest.NewLogger(t)),
 		bootstrap.WithFilesystem(fs),
 	)
 	ch, err := updater.Subscribe()
@@ -276,7 +276,7 @@ func TestStartClose(t *testing.T) {
 	updater := bootstrap.New(
 		mc,
 		bootstrap.WithConfig(cfg),
-		bootstrap.WithLogger(logtest.New(t)),
+		bootstrap.WithLogger(zaptest.NewLogger(t)),
 		bootstrap.WithFilesystem(fs),
 	)
 	ch, err := updater.Subscribe()
@@ -322,7 +322,7 @@ func TestPrune(t *testing.T) {
 	updater := bootstrap.New(
 		mc,
 		bootstrap.WithConfig(cfg),
-		bootstrap.WithLogger(logtest.New(t)),
+		bootstrap.WithLogger(zaptest.NewLogger(t)),
 		bootstrap.WithFilesystem(fs),
 		bootstrap.WithHttpClient(ts.Client()),
 	)
@@ -384,7 +384,7 @@ func TestDoIt(t *testing.T) {
 			updater := bootstrap.New(
 				mc,
 				bootstrap.WithConfig(cfg),
-				bootstrap.WithLogger(logtest.New(t)),
+				bootstrap.WithLogger(zaptest.NewLogger(t)),
 				bootstrap.WithFilesystem(fs),
 				bootstrap.WithHttpClient(ts.Client()),
 			)
@@ -421,7 +421,7 @@ func TestEmptyResponse(t *testing.T) {
 	updater := bootstrap.New(
 		mc,
 		bootstrap.WithConfig(cfg),
-		bootstrap.WithLogger(logtest.New(t)),
+		bootstrap.WithLogger(zaptest.NewLogger(t)),
 		bootstrap.WithFilesystem(fs),
 		bootstrap.WithHttpClient(ts.Client()),
 	)
@@ -492,7 +492,7 @@ func TestGetInvalidUpdate(t *testing.T) {
 			updater := bootstrap.New(
 				mc,
 				bootstrap.WithConfig(cfg),
-				bootstrap.WithLogger(logtest.New(t)),
+				bootstrap.WithLogger(zaptest.NewLogger(t)),
 				bootstrap.WithFilesystem(fs),
 				bootstrap.WithHttpClient(ts.Client()),
 			)
@@ -526,7 +526,7 @@ func TestNoNewUpdate(t *testing.T) {
 	updater := bootstrap.New(
 		mc,
 		bootstrap.WithConfig(cfg),
-		bootstrap.WithLogger(logtest.New(t)),
+		bootstrap.WithLogger(zaptest.NewLogger(t)),
 		bootstrap.WithFilesystem(fs),
 		bootstrap.WithHttpClient(ts.Client()),
 	)
@@ -647,7 +647,7 @@ func TestRequiredEpochs(t *testing.T) {
 			updater := bootstrap.New(
 				mc,
 				bootstrap.WithConfig(cfg),
-				bootstrap.WithLogger(logtest.New(t)),
+				bootstrap.WithLogger(zaptest.NewLogger(t)),
 				bootstrap.WithFilesystem(fs),
 				bootstrap.WithHttpClient(ts.Client()),
 			)
@@ -676,7 +676,7 @@ func TestIntegration(t *testing.T) {
 	updater := bootstrap.New(
 		mc,
 		bootstrap.WithConfig(cfg),
-		bootstrap.WithLogger(logtest.New(t)),
+		bootstrap.WithLogger(zaptest.NewLogger(t)),
 		bootstrap.WithFilesystem(fs),
 	)
 	ch, err := updater.Subscribe()
@@ -709,7 +709,7 @@ func TestClose(t *testing.T) {
 	updater := bootstrap.New(
 		mc,
 		bootstrap.WithConfig(cfg),
-		bootstrap.WithLogger(logtest.New(t)),
+		bootstrap.WithLogger(zaptest.NewLogger(t)),
 		bootstrap.WithFilesystem(fs),
 	)
 	ch, err := updater.Subscribe()
diff --git a/checkpoint/recovery.go b/checkpoint/recovery.go
index 97a77d5468..31df1cdff1 100644
--- a/checkpoint/recovery.go
+++ b/checkpoint/recovery.go
@@ -356,6 +356,10 @@ func checkpointData(fs afero.Fs, file string, newGenesis types.LayerID) (*recove
 		cAtx.ID = types.ATXID(types.BytesToHash(atx.ID))
 		cAtx.Epoch = types.EpochID(atx.Epoch)
 		cAtx.CommitmentATX = types.ATXID(types.BytesToHash(atx.CommitmentAtx))
+		if len(atx.MarriageAtx) == 32 {
+			marriageATXID := types.ATXID(atx.MarriageAtx)
+			cAtx.MarriageATX = &marriageATXID
+		}
 		cAtx.SmesherID = types.BytesToNodeID(atx.PublicKey)
 		cAtx.NumUnits = atx.NumUnits
 		cAtx.VRFNonce = types.VRFPostIndex(atx.VrfNonce)
diff --git a/checkpoint/recovery_test.go b/checkpoint/recovery_test.go
index b21f9e9d06..d67a259225 100644
--- a/checkpoint/recovery_test.go
+++ b/checkpoint/recovery_test.go
@@ -908,7 +908,8 @@ func TestRecover_OwnAtxInCheckpoint(t *testing.T) {
 	require.NoError(t, err)
 	atxid, err := hex.DecodeString("98e47278c1f58acfd2b670a730f28898f74eb140482a07b91ff81f9ff0b7d9f4")
 	require.NoError(t, err)
-	atx := newAtx(types.ATXID(atxid), types.EmptyATXID, nil, 3, 1, 0, nid)
+	atx := &types.ActivationTx{SmesherID: types.NodeID(nid)}
+	atx.SetID(types.ATXID(atxid))
 
 	cfg := &checkpoint.RecoverConfig{
 		GoldenAtx:   goldenAtx,
diff --git a/checkpoint/runner.go b/checkpoint/runner.go
index 2b72e236b0..7039aa54c0 100644
--- a/checkpoint/runner.go
+++ b/checkpoint/runner.go
@@ -78,10 +78,15 @@ func checkpointDB(
 		if mal, ok := malicious[catx.SmesherID]; ok && mal {
 			continue
 		}
+		var marriageAtx []byte
+		if catx.MarriageATX != nil {
+			marriageAtx = catx.MarriageATX.Bytes()
+		}
 		checkpoint.Data.Atxs = append(checkpoint.Data.Atxs, types.AtxSnapshot{
 			ID:             catx.ID.Bytes(),
 			Epoch:          catx.Epoch.Uint32(),
 			CommitmentAtx:  catx.CommitmentATX.Bytes(),
+			MarriageAtx:    marriageAtx,
 			VrfNonce:       uint64(catx.VRFNonce),
 			NumUnits:       catx.NumUnits,
 			BaseTickHeight: catx.BaseTickHeight,
diff --git a/checkpoint/runner_test.go b/checkpoint/runner_test.go
index f7009c24ec..472f62a8be 100644
--- a/checkpoint/runner_test.go
+++ b/checkpoint/runner_test.go
@@ -238,10 +238,15 @@ func newAtx(
 }
 
 func asAtxSnapshot(v *types.ActivationTx, cmt *types.ATXID) types.AtxSnapshot {
+	var marriageATX []byte
+	if v.MarriageATX != nil {
+		marriageATX = v.MarriageATX.Bytes()
+	}
 	return types.AtxSnapshot{
 		ID:             v.ID().Bytes(),
 		Epoch:          v.PublishEpoch.Uint32(),
 		CommitmentAtx:  cmt.Bytes(),
+		MarriageAtx:    marriageATX,
 		VrfNonce:       uint64(v.VRFNonce),
 		NumUnits:       v.NumUnits,
 		BaseTickHeight: v.BaseTickHeight,
@@ -375,3 +380,35 @@ func TestRunner_Generate_Error(t *testing.T) {
 		require.Error(t, err)
 	})
 }
+
+func TestRunner_Generate_PreservesMarriageATX(t *testing.T) {
+	t.Parallel()
+	db := sql.InMemory()
+
+	require.NoError(t, accounts.Update(db, &types.Account{Address: types.Address{1, 1}}))
+
+	atx := &types.ActivationTx{
+		CommitmentATX: &types.ATXID{1, 2, 3, 4, 5},
+		MarriageATX:   &types.ATXID{6, 7, 8, 9},
+		SmesherID:     types.RandomNodeID(),
+		NumUnits:      4,
+	}
+	atx.SetID(types.RandomATXID())
+	require.NoError(t, atxs.Add(db, atx, types.AtxBlob{}))
+	require.NoError(t, atxs.SetUnits(db, atx.ID(), atx.SmesherID, atx.NumUnits))
+
+	fs := afero.NewMemMapFs()
+	dir, err := afero.TempDir(fs, "", "Generate")
+	require.NoError(t, err)
+
+	err = checkpoint.Generate(context.Background(), fs, db, dir, 5, 2)
+	require.NoError(t, err)
+
+	file, err := fs.Open(checkpoint.SelfCheckpointFilename(dir, 5))
+	require.NoError(t, err)
+	defer file.Close()
+
+	var checkpoint types.Checkpoint
+	require.NoError(t, json.NewDecoder(file).Decode(&checkpoint))
+	require.Equal(t, atx.MarriageATX.Bytes(), checkpoint.Data.Atxs[0].MarriageAtx)
+}
diff --git a/common/types/activation.go b/common/types/activation.go
index 41112efc4c..4a1da34c15 100644
--- a/common/types/activation.go
+++ b/common/types/activation.go
@@ -178,7 +178,9 @@ type ActivationTx struct {
 	PrevATXID ATXID
 
 	// CommitmentATX is the ATX used in the commitment for initializing the PoST of the node.
-	CommitmentATX  *ATXID
+	CommitmentATX *ATXID
+	// The marriage ATX, used in merged ATXs only.
+	MarriageATX    *ATXID
 	Coinbase       Address
 	NumUnits       uint32 // the minimum number of space units in this and the previous ATX
 	BaseTickHeight uint64
@@ -231,6 +233,9 @@ func (atx *ActivationTx) MarshalLogObject(encoder log.ObjectEncoder) error {
 	if atx.CommitmentATX != nil {
 		encoder.AddString("commitment_atx_id", atx.CommitmentATX.String())
 	}
+	if atx.MarriageATX != nil {
+		encoder.AddString("marriage_atx_id", atx.MarriageATX.String())
+	}
 	encoder.AddUint64("vrf_nonce", uint64(atx.VRFNonce))
 	encoder.AddString("coinbase", atx.Coinbase.String())
 	encoder.AddUint32("epoch", atx.PublishEpoch.Uint32())
diff --git a/common/types/checkpoint.go b/common/types/checkpoint.go
index 7f04b35a87..81184e6b30 100644
--- a/common/types/checkpoint.go
+++ b/common/types/checkpoint.go
@@ -17,6 +17,7 @@ type AtxSnapshot struct {
 	ID             []byte `json:"id"`
 	Epoch          uint32 `json:"epoch"`
 	CommitmentAtx  []byte `json:"commitmentAtx"`
+	MarriageAtx    []byte `json:"marriageAtx"`
 	VrfNonce       uint64 `json:"vrfNonce"`
 	BaseTickHeight uint64 `json:"baseTickHeight"`
 	TickCount      uint64 `json:"tickCount"`
diff --git a/go.mod b/go.mod
index b8652db3cc..931e19278b 100644
--- a/go.mod
+++ b/go.mod
@@ -39,7 +39,7 @@ require (
 	github.com/santhosh-tekuri/jsonschema/v5 v5.3.1
 	github.com/seehuhn/mt19937 v1.0.0
 	github.com/slok/go-http-metrics v0.12.0
-	github.com/spacemeshos/api/release/go v1.50.0
+	github.com/spacemeshos/api/release/go v1.51.0
 	github.com/spacemeshos/economics v0.1.3
 	github.com/spacemeshos/fixed v0.1.1
 	github.com/spacemeshos/go-scale v1.2.0
diff --git a/go.sum b/go.sum
index 42c9cad502..be27867b00 100644
--- a/go.sum
+++ b/go.sum
@@ -602,8 +602,8 @@ github.com/sourcegraph/annotate v0.0.0-20160123013949-f4cad6c6324d/go.mod h1:Udh
 github.com/sourcegraph/conc v0.3.0 h1:OQTbbt6P72L20UqAkXXuLOj79LfEanQ+YQFNpLA9ySo=
 github.com/sourcegraph/conc v0.3.0/go.mod h1:Sdozi7LEKbFPqYX2/J+iBAM6HpqSLTASQIKqDmF7Mt0=
 github.com/sourcegraph/syntaxhighlight v0.0.0-20170531221838-bd320f5d308e/go.mod h1:HuIsMU8RRBOtsCgI77wP899iHVBQpCmg4ErYMZB+2IA=
-github.com/spacemeshos/api/release/go v1.50.0 h1:M7Usg/LxymscwqYO7/Doyb+sU4lS1e+JIsSgqTDGk/0=
-github.com/spacemeshos/api/release/go v1.50.0/go.mod h1:PvgDpjfwkZLVVNExYG7wDNzgMqT3p+ppfTU2UESSF9U=
+github.com/spacemeshos/api/release/go v1.51.0 h1:MSKRIUiXBAoDrj2Lj24q9g52ZaSIC3I0UH/Y0Oaz95o=
+github.com/spacemeshos/api/release/go v1.51.0/go.mod h1:Qr/pVPMmN5Q5qLHSXqVMDKDCu6LkHWzGPNflylE0u00=
 github.com/spacemeshos/economics v0.1.3 h1:ACkq3mTebIky4Zwbs9SeSSRZrUCjU/Zk0wq9Z0BTh2A=
 github.com/spacemeshos/economics v0.1.3/go.mod h1:FH7u0FzTIm6Kpk+X5HOZDvpkgNYBKclmH86rVwYaDAo=
 github.com/spacemeshos/fixed v0.1.1 h1:N1y4SUpq1EV+IdJrWJwUCt1oBFzeru/VKVcBsvPc2Fk=
diff --git a/node/node.go b/node/node.go
index 7ead90aec3..e789d09c1e 100644
--- a/node/node.go
+++ b/node/node.go
@@ -784,7 +784,7 @@ func (app *App) initServices(ctx context.Context) error {
 	app.updater = bootstrap.New(
 		app.clock,
 		bootstrap.WithConfig(bscfg),
-		bootstrap.WithLogger(app.addLogger(BootstrapLogger, lg)),
+		bootstrap.WithLogger(app.addLogger(BootstrapLogger, lg).Zap()),
 	)
 	if app.Config.Certificate.CommitteeSize == 0 {
 		app.log.With().Warning("certificate committee size is not set, defaulting to hare committee size",
@@ -1558,8 +1558,7 @@ func (app *App) grpcService(svc grpcserver.Service, lg log.Log) (grpcserver.Serv
 	case v2alpha1.Network:
 		service := v2alpha1.NewNetworkService(
 			app.clock.GenesisTime(),
-			app.Config.Genesis.GenesisID(),
-			app.Config.LayerDuration)
+			app.Config)
 		app.grpcServices[svc] = service
 		return service, nil
 	case v2alpha1.Node:
diff --git a/sql/atxs/atxs.go b/sql/atxs/atxs.go
index 408e450c75..5e14cddde1 100644
--- a/sql/atxs/atxs.go
+++ b/sql/atxs/atxs.go
@@ -22,7 +22,8 @@ const (
 // filters that refer to the id column.
 const fieldsQuery = `select
 atxs.id, atxs.nonce, atxs.base_tick_height, atxs.tick_count, atxs.pubkey, atxs.effective_num_units,
-atxs.received, atxs.epoch, atxs.sequence, atxs.coinbase, atxs.validity, atxs.prev_id, atxs.commitment_atx, atxs.weight`
+atxs.received, atxs.epoch, atxs.sequence, atxs.coinbase, atxs.validity, atxs.prev_id, atxs.commitment_atx, atxs.weight,
+atxs.marriage_atx`
 
 const fullQuery = fieldsQuery + ` from atxs`
 
@@ -62,6 +63,10 @@ func decoder(fn decoderCallback) sql.Decoder {
 			stmt.ColumnBytes(12, a.CommitmentATX[:])
 		}
 		a.Weight = uint64(stmt.ColumnInt64(13))
+		if stmt.ColumnType(14) != sqlite.SQLITE_NULL {
+			a.MarriageATX = new(types.ATXID)
+			stmt.ColumnBytes(14, a.MarriageATX[:])
+		}
 
 		return fn(&a)
 	}
@@ -425,8 +430,6 @@ func Add(db sql.Executor, atx *types.ActivationTx, blob types.AtxBlob) error {
 		stmt.BindInt64(3, int64(atx.NumUnits))
 		if atx.CommitmentATX != nil {
 			stmt.BindBytes(4, atx.CommitmentATX.Bytes())
-		} else {
-			stmt.BindNull(4)
 		}
 		stmt.BindInt64(5, int64(atx.VRFNonce))
 		stmt.BindBytes(6, atx.SmesherID.Bytes())
@@ -438,17 +441,18 @@ func Add(db sql.Executor, atx *types.ActivationTx, blob types.AtxBlob) error {
 		stmt.BindInt64(12, int64(atx.Validity()))
 		if atx.PrevATXID != types.EmptyATXID {
 			stmt.BindBytes(13, atx.PrevATXID.Bytes())
-		} else {
-			stmt.BindNull(13)
 		}
 		stmt.BindInt64(14, int64(atx.Weight))
+		if atx.MarriageATX != nil {
+			stmt.BindBytes(15, atx.MarriageATX.Bytes())
+		}
 	}
 
 	_, err := db.Exec(`
 		insert into atxs (id, epoch, effective_num_units, commitment_atx, nonce,
 			 pubkey, received, base_tick_height, tick_count, sequence, coinbase,
-			 validity, prev_id, weight)
-		values (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11, ?12, ?13, ?14)`, enc, nil)
+			 validity, prev_id, weight, marriage_atx)
+		values (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11, ?12, ?13, ?14, ?15)`, enc, nil)
 	if err != nil {
 		return fmt.Errorf("insert ATX ID %v: %w", atx.ID(), err)
 	}
@@ -539,6 +543,7 @@ type CheckpointAtx struct {
 	ID             types.ATXID
 	Epoch          types.EpochID
 	CommitmentATX  types.ATXID
+	MarriageATX    *types.ATXID
 	VRFNonce       types.VRFPostIndex
 	BaseTickHeight uint64
 	TickCount      uint64
@@ -571,16 +576,21 @@ func LatestN(db sql.Executor, n int) ([]CheckpointAtx, error) {
 		catx.Sequence = uint64(stmt.ColumnInt64(6))
 		stmt.ColumnBytes(7, catx.Coinbase[:])
 		catx.VRFNonce = types.VRFPostIndex(stmt.ColumnInt64(8))
-		catx.Units = make(map[types.NodeID]uint32)
+		if stmt.ColumnType(9) != sqlite.SQLITE_NULL {
+			catx.MarriageATX = new(types.ATXID)
+			stmt.ColumnBytes(9, catx.MarriageATX[:])
+		}
 		rst = append(rst, catx)
 		return true
 	}
 
 	rows, err := db.Exec(`
-		select id, epoch, effective_num_units, base_tick_height, tick_count, pubkey, sequence, coinbase, nonce
+		select
+		id, epoch, effective_num_units, base_tick_height, tick_count, pubkey, sequence, coinbase, nonce, marriage_atx
 		from (
 			select row_number() over (partition by pubkey order by epoch desc) RowNum,
-			id, epoch, effective_num_units, base_tick_height, tick_count, pubkey, sequence, coinbase, nonce
+			id, epoch, effective_num_units, base_tick_height, tick_count, pubkey, sequence, coinbase, nonce,
+			marriage_atx
 			from atxs
 		)
 		where RowNum <= ?1 order by pubkey;`, enc, dec)
@@ -616,12 +626,15 @@ func AddCheckpointed(db sql.Executor, catx *CheckpointAtx) error {
 		stmt.BindInt64(8, int64(catx.Sequence))
 		stmt.BindBytes(9, catx.SmesherID.Bytes())
 		stmt.BindBytes(10, catx.Coinbase.Bytes())
+		if catx.MarriageATX != nil {
+			stmt.BindBytes(11, catx.MarriageATX.Bytes())
+		}
 	}
 
 	_, err := db.Exec(`
 		insert into atxs (id, epoch, effective_num_units, commitment_atx, nonce,
-			base_tick_height, tick_count, sequence, pubkey, coinbase, received)
-		values (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, 0)`, enc, nil)
+			base_tick_height, tick_count, sequence, pubkey, coinbase, marriage_atx, received)
+		values (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11, 0)`, enc, nil)
 	if err != nil {
 		return fmt.Errorf("insert checkpoint ATX %v: %w", catx.ID, err)
 	}
@@ -803,7 +816,7 @@ func IterateAtxsWithMalfeasance(
 		func(s *sql.Statement) { s.BindInt64(1, int64(publish)) },
 		func(s *sql.Statement) bool {
 			return decoder(func(atx *types.ActivationTx) bool {
-				return fn(atx, s.ColumnInt(14) != 0)
+				return fn(atx, s.ColumnInt(15) != 0)
 			})(s)
 		},
 	)
@@ -891,6 +904,38 @@ func Units(db sql.Executor, atxID types.ATXID, nodeID types.NodeID) (uint32, err
 	return units, err
 }
 
+// FindDoublePublish finds 2 distinct ATXIDs that the given identity contributed PoST to in the given epoch.
+//
+// It is guaranteed to return 2 distinct ATXs when the error is nil.
+// It works by finding an ATX in the given epoch that has a PoST contribution from the given identity.
+// - `epoch` is looked up in the `atxs` table by matching atxid.
+func FindDoublePublish(db sql.Executor, nodeID types.NodeID, epoch types.EpochID) ([]types.ATXID, error) {
+	var ids []types.ATXID
+	rows, err := db.Exec(`
+		SELECT p.atxid
+		FROM posts p
+		INNER JOIN atxs a ON p.atxid = a.id
+		WHERE p.pubkey = ?1 AND a.epoch = ?2;`,
+		func(stmt *sql.Statement) {
+			stmt.BindBytes(1, nodeID.Bytes())
+			stmt.BindInt64(2, int64(epoch))
+		},
+		func(stmt *sql.Statement) bool {
+			var id types.ATXID
+			stmt.ColumnBytes(0, id[:])
+			ids = append(ids, id)
+			return len(ids) < 2
+		},
+	)
+	if err != nil {
+		return nil, err
+	}
+	if rows != 2 {
+		return nil, sql.ErrNotFound
+	}
+	return ids, nil
+}
+
 func AllUnits(db sql.Executor, id types.ATXID) (map[types.NodeID]uint32, error) {
 	units := make(map[types.NodeID]uint32)
 	rows, err := db.Exec(
@@ -963,3 +1008,28 @@ func AtxWithPrevious(db sql.Executor, prev types.ATXID, id types.NodeID) (types.
 	}
 	return atxid, nil
 }
+
+// Find 2 distinct merged ATXs (having the same marriage ATX) in the same epoch.
+func MergeConflict(db sql.Executor, marriage types.ATXID, publish types.EpochID) ([]types.ATXID, error) {
+	var ids []types.ATXID
+	rows, err := db.Exec(`
+		SELECT id FROM atxs WHERE marriage_atx = ?1 and epoch = ?2;`,
+		func(stmt *sql.Statement) {
+			stmt.BindBytes(1, marriage.Bytes())
+			stmt.BindInt64(2, int64(publish))
+		},
+		func(stmt *sql.Statement) bool {
+			var id types.ATXID
+			stmt.ColumnBytes(0, id[:])
+			ids = append(ids, id)
+			return len(ids) < 2
+		},
+	)
+	if err != nil {
+		return nil, err
+	}
+	if rows != 2 {
+		return nil, sql.ErrNotFound
+	}
+	return ids, nil
+}
diff --git a/sql/atxs/atxs_test.go b/sql/atxs/atxs_test.go
index d3ac0dd3de..1dd1914968 100644
--- a/sql/atxs/atxs_test.go
+++ b/sql/atxs/atxs_test.go
@@ -1201,3 +1201,132 @@ func Test_AtxWithPrevious(t *testing.T) {
 		require.Equal(t, atx2.ID(), id)
 	})
 }
+
+func Test_FindDoublePublish(t *testing.T) {
+	t.Parallel()
+	sig, err := signing.NewEdSigner()
+	require.NoError(t, err)
+	t.Run("no atxs", func(t *testing.T) {
+		t.Parallel()
+		db := sql.InMemory()
+		_, err := atxs.FindDoublePublish(db, types.RandomNodeID(), 0)
+		require.ErrorIs(t, err, sql.ErrNotFound)
+	})
+
+	t.Run("no double publish", func(t *testing.T) {
+		t.Parallel()
+		db := sql.InMemory()
+
+		// one atx
+		atx0, blob := newAtx(t, sig, withPublishEpoch(1))
+		require.NoError(t, atxs.Add(db, atx0, blob))
+		require.NoError(t, atxs.SetUnits(db, atx0.ID(), atx0.SmesherID, 10))
+
+		_, err = atxs.FindDoublePublish(db, atx0.SmesherID, atx0.PublishEpoch)
+		require.ErrorIs(t, err, sql.ErrNotFound)
+
+		// two atxs in different epochs
+		atx1, blob := newAtx(t, sig, withPublishEpoch(atx0.PublishEpoch+1))
+		require.NoError(t, atxs.Add(db, atx1, blob))
+		require.NoError(t, atxs.SetUnits(db, atx1.ID(), atx0.SmesherID, 10))
+
+		_, err = atxs.FindDoublePublish(db, atx0.SmesherID, atx0.PublishEpoch)
+		require.ErrorIs(t, err, sql.ErrNotFound)
+	})
+	t.Run("double publish", func(t *testing.T) {
+		t.Parallel()
+		db := sql.InMemory()
+
+		atx0, blob := newAtx(t, sig)
+		require.NoError(t, atxs.Add(db, atx0, blob))
+		require.NoError(t, atxs.SetUnits(db, atx0.ID(), atx0.SmesherID, 10))
+
+		atx1, blob := newAtx(t, sig)
+		require.NoError(t, atxs.Add(db, atx1, blob))
+		require.NoError(t, atxs.SetUnits(db, atx1.ID(), atx0.SmesherID, 10))
+
+		atxids, err := atxs.FindDoublePublish(db, atx0.SmesherID, atx0.PublishEpoch)
+		require.NoError(t, err)
+		require.ElementsMatch(t, []types.ATXID{atx0.ID(), atx1.ID()}, atxids)
+
+		// filters by epoch
+		_, err = atxs.FindDoublePublish(db, atx0.SmesherID, atx0.PublishEpoch+1)
+		require.ErrorIs(t, err, sql.ErrNotFound)
+	})
+	t.Run("double publish different smesher", func(t *testing.T) {
+		t.Parallel()
+		db := sql.InMemory()
+
+		atx0Signer, err := signing.NewEdSigner()
+		require.NoError(t, err)
+
+		atx0, blob := newAtx(t, atx0Signer)
+		require.NoError(t, atxs.Add(db, atx0, blob))
+		require.NoError(t, atxs.SetUnits(db, atx0.ID(), atx0.SmesherID, 10))
+		require.NoError(t, atxs.SetUnits(db, atx0.ID(), sig.NodeID(), 10))
+
+		atx1Signer, err := signing.NewEdSigner()
+		require.NoError(t, err)
+
+		atx1, blob := newAtx(t, atx1Signer)
+		require.NoError(t, atxs.Add(db, atx1, blob))
+		require.NoError(t, atxs.SetUnits(db, atx1.ID(), atx1.SmesherID, 10))
+		require.NoError(t, atxs.SetUnits(db, atx1.ID(), sig.NodeID(), 10))
+
+		atxIDs, err := atxs.FindDoublePublish(db, sig.NodeID(), atx0.PublishEpoch)
+		require.NoError(t, err)
+		require.ElementsMatch(t, []types.ATXID{atx0.ID(), atx1.ID()}, atxIDs)
+	})
+}
+
+func Test_MergeConflict(t *testing.T) {
+	t.Parallel()
+	t.Run("no atxs", func(t *testing.T) {
+		t.Parallel()
+		db := sql.InMemory()
+		_, err := atxs.MergeConflict(db, types.RandomATXID(), 0)
+		require.ErrorIs(t, err, sql.ErrNotFound)
+	})
+	t.Run("no conflict", func(t *testing.T) {
+		t.Parallel()
+		db := sql.InMemory()
+		marriage := types.RandomATXID()
+
+		atx := types.ActivationTx{MarriageATX: &marriage}
+		atx.SetID(types.RandomATXID())
+		require.NoError(t, atxs.Add(db, &atx, types.AtxBlob{}))
+
+		_, err := atxs.MergeConflict(db, types.RandomATXID(), atx.PublishEpoch)
+		require.ErrorIs(t, err, sql.ErrNotFound)
+	})
+	t.Run("finds conflict", func(t *testing.T) {
+		t.Parallel()
+		db := sql.InMemory()
+		marriage := types.RandomATXID()
+
+		atx0 := types.ActivationTx{MarriageATX: &marriage}
+		atx0.SetID(types.RandomATXID())
+		require.NoError(t, atxs.Add(db, &atx0, types.AtxBlob{}))
+
+		atx1 := types.ActivationTx{MarriageATX: &marriage}
+		atx1.SetID(types.RandomATXID())
+		require.NoError(t, atxs.Add(db, &atx1, types.AtxBlob{}))
+
+		ids, err := atxs.MergeConflict(db, marriage, atx0.PublishEpoch)
+		require.NoError(t, err)
+		require.ElementsMatch(t, []types.ATXID{atx0.ID(), atx1.ID()}, ids)
+
+		// filters by epoch
+		_, err = atxs.MergeConflict(db, types.RandomATXID(), 8)
+		require.ErrorIs(t, err, sql.ErrNotFound)
+
+		// returns only 2 ATXs
+		atx2 := types.ActivationTx{MarriageATX: &marriage}
+		atx2.SetID(types.RandomATXID())
+		require.NoError(t, atxs.Add(db, &atx2, types.AtxBlob{}))
+
+		ids, err = atxs.MergeConflict(db, marriage, atx0.PublishEpoch)
+		require.NoError(t, err)
+		require.Len(t, ids, 2)
+	})
+}
diff --git a/sql/migrations/state/0020_atx_merge.sql b/sql/migrations/state/0020_atx_merge.sql
index 17bcda9c83..8dbff567c0 100644
--- a/sql/migrations/state/0020_atx_merge.sql
+++ b/sql/migrations/state/0020_atx_merge.sql
@@ -1,5 +1,6 @@
 -- Changes required to handle merged ATXs
 
+ALTER TABLE atxs ADD COLUMN marriage_atx CHAR(32);
 ALTER TABLE atxs ADD COLUMN weight INTEGER;
 UPDATE atxs SET weight = effective_num_units * tick_count;