diff --git a/sigmastate/src/main/scala/org/ergoplatform/ErgoBoxCandidate.scala b/sigmastate/src/main/scala/org/ergoplatform/ErgoBoxCandidate.scala
index 1b7638f233..bf13b8d9c8 100644
--- a/sigmastate/src/main/scala/org/ergoplatform/ErgoBoxCandidate.scala
+++ b/sigmastate/src/main/scala/org/ergoplatform/ErgoBoxCandidate.scala
@@ -188,6 +188,10 @@ object ErgoBoxCandidate {
       val value = r.getULong()                  // READ
       val tree = DefaultSerializer.deserializeErgoTree(r, SigmaSerializer.MaxPropositionSize)  // READ
       val creationHeight = r.getUIntExact       // READ
+      // NO-FORK: ^ in v5.x getUIntExact may throw Int overflow exception
+      // in v4.x r.getUInt().toInt is used and may return negative Int instead of the overflow
+      // and ErgoBoxCandidate with negative creation height is created, which is then invalidated
+      // during transaction validation. See validation rule # 122 in the Ergo node (ValidationRules.scala)
       val nTokens = r.getUByte()                // READ
       val tokenIds = safeNewArray[Array[Byte]](nTokens)
       val tokenAmounts = safeNewArray[Long](nTokens)
@@ -195,6 +199,9 @@ object ErgoBoxCandidate {
         val nDigests = digestsInTx.length
         cfor(0)(_ < nTokens, _ + 1) { i =>
           val digestIndex = r.getUIntExact    // READ
+          // NO-FORK: in v5.x getUIntExact throws Int overflow exception
+          // in v4.x r.getUInt().toInt is used and may return negative Int in which case
+          // the error below is thrown
           if (digestIndex < 0 || digestIndex >= nDigests)
             sys.error(s"failed to find token id with index $digestIndex")
           val amount = r.getULong()           // READ
diff --git a/sigmastate/src/main/scala/org/ergoplatform/ErgoLikeTransaction.scala b/sigmastate/src/main/scala/org/ergoplatform/ErgoLikeTransaction.scala
index 683602dcc8..f1c986fca1 100644
--- a/sigmastate/src/main/scala/org/ergoplatform/ErgoLikeTransaction.scala
+++ b/sigmastate/src/main/scala/org/ergoplatform/ErgoLikeTransaction.scala
@@ -162,6 +162,9 @@ object ErgoLikeTransactionSerializer extends SigmaSerializer[ErgoLikeTransaction
 
     // parse distinct ids of tokens in transaction outputs
     val tokensCount = r.getUIntExact
+    // NO-FORK: in v5.x getUIntExact may throw Int overflow exception
+    // in v4.x r.getUInt().toInt is used and may return negative Int instead of the overflow
+    // in which case the array allocation will throw NegativeArraySizeException
     val tokens = safeNewArray[Array[Byte]](tokensCount)
     cfor(0)(_ < tokensCount, _ + 1) { i =>
       tokens(i) = r.getBytes(TokenId.size)
diff --git a/sigmastate/src/main/scala/org/ergoplatform/validation/SigmaValidationSettingsSerializer.scala b/sigmastate/src/main/scala/org/ergoplatform/validation/SigmaValidationSettingsSerializer.scala
index 2c66b05e71..1e2b8b352a 100644
--- a/sigmastate/src/main/scala/org/ergoplatform/validation/SigmaValidationSettingsSerializer.scala
+++ b/sigmastate/src/main/scala/org/ergoplatform/validation/SigmaValidationSettingsSerializer.scala
@@ -4,6 +4,7 @@ import sigmastate.serialization.SigmaSerializer
 import sigmastate.utils.{SigmaByteReader, SigmaByteWriter}
 import scalan.util.Extensions.{IntOps,LongOps}
 
+// TODO v5.x: remove unused class and related json encoders
 /** The rules are serialized ordered by ruleId.
   * This serializer preserves roundtrip identity `deserialize(serialize(_)) = identity`
   * however it may not preserve `serialize(deserialize(_)) = identity` */
@@ -19,7 +20,8 @@ object SigmaValidationSettingsSerializer extends SigmaSerializer[SigmaValidation
   }
 
   override def parse(r: SigmaByteReader): SigmaValidationSettings = {
-    val nRules = r.getUIntExact
+    val nRules = r.getUInt().toInt
+    // Note, when nRules < 0 as a result of Int overflow, the loop is empty
     val parsed = (0 until nRules).map { _ =>
       val ruleId = r.getUShort().toShortExact
       val status = RuleStatusSerializer.parse(r)
diff --git a/sigmastate/src/main/scala/sigmastate/AvlTreeData.scala b/sigmastate/src/main/scala/sigmastate/AvlTreeData.scala
index ae94121920..81aafa1a19 100644
--- a/sigmastate/src/main/scala/sigmastate/AvlTreeData.scala
+++ b/sigmastate/src/main/scala/sigmastate/AvlTreeData.scala
@@ -92,8 +92,11 @@ object AvlTreeData {
     override def parse(r: SigmaByteReader): AvlTreeData = {
       val digest = r.getBytes(DigestSize)
       val tf = AvlTreeFlags(r.getByte())
-      val keyLength = r.getUIntExact
-      val valueLengthOpt = r.getOption(r.getUIntExact)
+      val keyLength = r.getUInt().toInt
+      val valueLengthOpt = r.getOption(r.getUInt().toInt)
+      // Note, when keyLength and valueLengthOpt < 0 as a result of Int overflow,
+      // the deserializer succeeds with invalid AvlTreeData
+      // but still some AvlTree operations (remove_eval, update_eval, contains_eval) won't throw
       AvlTreeData(ADDigest @@ digest, tf, keyLength, valueLengthOpt)
     }
   }
diff --git a/sigmastate/src/main/scala/sigmastate/Values.scala b/sigmastate/src/main/scala/sigmastate/Values.scala
index 4667097dbe..d42242ccae 100644
--- a/sigmastate/src/main/scala/sigmastate/Values.scala
+++ b/sigmastate/src/main/scala/sigmastate/Values.scala
@@ -890,8 +890,6 @@ object Values {
     def tpe = SBox
   }
 
-  // TODO refactor: only Constant make sense to inherit from EvaluatedValue
-
   /** ErgoTree node which converts a collection of expressions into a tuple of data values
     * of different types. Each data value of the resulting collection is obtained by
     * evaluating the corresponding expression in `items`. All items may have different
@@ -899,10 +897,19 @@ object Values {
     *
     * @param items source collection of expressions
     */
-  case class Tuple(items: IndexedSeq[Value[SType]]) extends Value[STuple] {
+  case class Tuple(items: IndexedSeq[Value[SType]])
+      extends EvaluatedValue[STuple]  // note, this superclass is required as Tuple can be in a register
+         with EvaluatedCollection[SAny.type, STuple] {
     override def companion = Tuple
     override lazy val tpe = STuple(items.map(_.tpe))
     override def opType: SFunc = ???
+    override def elementType: SAny.type = SAny
+
+    override lazy val value = {
+      val xs = items.cast[EvaluatedValue[SAny.type]].map(_.value)
+      Colls.fromArray(xs.toArray(SAny.classTag.asInstanceOf[ClassTag[SAny.WrappedType]]))(RType.AnyType)
+    }
+
     protected final override def eval(env: DataEnv)(implicit E: ErgoTreeEvaluator): Any = {
       // in v5.0 version we support only tuples of 2 elements to be equivalent with v4.x
       if (items.length != 2)
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/BlockValueSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/BlockValueSerializer.scala
index 7348156f96..52c6137869 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/BlockValueSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/BlockValueSerializer.scala
@@ -26,8 +26,12 @@ case class BlockValueSerializer(cons: (IndexedSeq[BlockItem], Value[SType]) => V
 
   override def parse(r: SigmaByteReader): Value[SType] = {
     val itemsSize = r.getUIntExact
-    val values: IndexedSeq[BlockItem] = if (itemsSize == 0)
+    // NO-FORK: in v5.x getUIntExact may throw Int overflow exception
+    // in v4.x r.getUInt().toInt is used and may return negative Int instead of the overflow
+    // in which case the array allocation will throw NegativeArraySizeException
+    val values: IndexedSeq[BlockItem] = if (itemsSize == 0) {
       BlockItem.EmptySeq
+    }
     else {
       // HOTSPOT:: allocate new array only if it is not empty
       val buf = safeNewArray[BlockItem](itemsSize)
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ConstantPlaceholderSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/ConstantPlaceholderSerializer.scala
index c3b834d00e..803f17079f 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ConstantPlaceholderSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ConstantPlaceholderSerializer.scala
@@ -15,6 +15,9 @@ case class ConstantPlaceholderSerializer(cons: (Int, SType) => Value[SType])
 
   override def parse(r: SigmaByteReader): Value[SType] = {
     val id = r.getUIntExact
+    // NO-FORK: in v5.x getUIntExact may throw Int overflow exception
+    // in v4.x r.getUInt().toInt is used and may return negative Int instead of the overflow
+    // in which case the constantStore.get will throw ArrayIndexOutOfBoundsException
     val constant = r.constantStore.get(id)
     if (r.resolvePlaceholdersToConstants)
       constant
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/DataSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/DataSerializer.scala
index 3071334c8d..1cff3961d3 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/DataSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/DataSerializer.scala
@@ -100,6 +100,9 @@ object DataSerializer {
       case SLong => r.getLong()
       case SString =>
         val size = r.getUIntExact
+        // NO-FORK: in v5.x getUIntExact may throw Int overflow exception
+        // in v4.x r.getUInt().toInt is used and may return negative Int instead of the overflow
+        // in which case the getBytes will throw NegativeArraySizeException
         val bytes = r.getBytes(size)
         new String(bytes, StandardCharsets.UTF_8)
       case SBigInt =>
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ErgoTreeSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/ErgoTreeSerializer.scala
index 06b39bc4eb..35d760b459 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ErgoTreeSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ErgoTreeSerializer.scala
@@ -207,7 +207,20 @@ class ErgoTreeSerializer {
     val header = r.getByte()
     CheckHeaderSizeBit(header)
     val sizeOpt = if (ErgoTree.hasSize(header)) {
-      Some(r.getUIntExact)
+      val size = r.getUInt().toInt
+      // Note, when size < 0 as a result of Int overflow nothing happens here and later
+      // when deserialization proceeds normally as sizeOpt is not used on this pass.
+      // However, when ValidationException is thrown in deserializeErgoTree this negative
+      // tree size value will be used in
+      // val val numBytes = bodyPos - startPos + treeSize
+      //            r.position = startPos
+      //            val bytes = r.getBytes(numBytes) = bodyPos - startPos + treeSize
+      // val bytes = r.getBytes(numBytes)
+      // If numBytes < 0 then it throws on getBytes and the whole deserialization fails
+      // On the other hand if numBytes >= 0 then UnparsedErgoTree will be created.
+      // The Reader however will be in some unpredictable state, as not all ErgoTree bytes
+      // are consumed.
+      Some(size)
     } else
       None
     (header, sizeOpt)
@@ -221,7 +234,10 @@ class ErgoTreeSerializer {
   private def deserializeConstants(header: Byte, r: SigmaByteReader): IndexedSeq[Constant[SType]] = {
     val constants: IndexedSeq[Constant[SType]] =
       if (ErgoTree.isConstantSegregation(header)) {
-        val nConsts = r.getUIntExact
+        val nConsts = r.getUInt().toInt
+        // Note, when nConsts < 0 as a result of Int overflow, the empty seq is returned
+        // deserialization will succeed
+
         if (nConsts > 0) {
           // HOTSPOT:: allocate new array only if it is not empty
           val res = safeNewArray[Constant[SType]](nConsts)
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/FuncValueSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/FuncValueSerializer.scala
index 9e84acddf5..5fe2b481fe 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/FuncValueSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/FuncValueSerializer.scala
@@ -28,9 +28,15 @@ case class FuncValueSerializer(cons: (IndexedSeq[(Int, SType)], Value[SType]) =>
 
   override def parse(r: SigmaByteReader): Value[SType] = {
     val argsSize = r.getUIntExact
+    // NO-FORK: in v5.x getUIntExact may throw Int overflow exception
+    // in v4.x r.getUInt().toInt is used and may return negative Int instead of the overflow
+    // in which case the array allocation will throw NegativeArraySizeException
     val args = safeNewArray[(Int, SType)](argsSize)
     cfor(0)(_ < argsSize, _ + 1) { i =>
-      val id = r.getUIntExact
+      val id = r.getUInt().toInt
+      // Note, when id < 0 as a result of Int overflow, the r.valDefTypeStore(id) won't throw
+      // More over evaluation of such FuncValue will not throw either if the body contains
+      // ValUse with the same negative id
       val tpe = r.getType()
       r.valDefTypeStore(id) = tpe
       args(i) = (id, tpe)
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ValDefSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/ValDefSerializer.scala
index 8a3394ee89..8a7d8d37bb 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ValDefSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ValDefSerializer.scala
@@ -31,6 +31,10 @@ case class ValDefSerializer(override val opDesc: ValueCompanion) extends ValueSe
 
   override def parse(r: SigmaByteReader): Value[SType] = {
     val id = r.getUIntExact
+    // NO-FORK: in v5.x getUIntExact may throw Int overflow exception
+    // in v4.x r.getUInt().toInt is used and may return negative Int instead of the overflow
+    // When id < 0 as a result of Int overflow, the r.valDefTypeStore(id) won't throw
+    // but ValDef constructor fails on require(id >= 0, "id must be >= 0")
     val tpeArgs: Seq[STypeVar] = opCode match {
       case FunDefCode =>
         val nTpeArgs = r.getByte()
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/ValUseSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/ValUseSerializer.scala
index 3daaad877f..523139c3ab 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/ValUseSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/ValUseSerializer.scala
@@ -12,7 +12,12 @@ case class ValUseSerializer(cons: (Int, SType) => Value[SType]) extends ValueSer
   }
 
   override def parse(r: SigmaByteReader): Value[SType] = {
-    val id = r.getUIntExact
+    val id = r.getUInt.toInt
+    // Note, when id < 0 as a result of Int overflow, the r.valDefTypeStore(id) won't throw
+    // and also ValUse node will be created, but then its evaluation will throw (because
+    // there will be no ValDef with negative id in the env.
+    // However, in general, there is no guarantee that this ValUse will ever be executed
+    // as it may be in an `if` branch.
     val tpe = r.valDefTypeStore(id)
     cons(id, tpe)
   }
diff --git a/sigmastate/src/main/scala/sigmastate/serialization/transformers/SigmaTransformerSerializer.scala b/sigmastate/src/main/scala/sigmastate/serialization/transformers/SigmaTransformerSerializer.scala
index c8fe96e1bb..e6a1d9c264 100644
--- a/sigmastate/src/main/scala/sigmastate/serialization/transformers/SigmaTransformerSerializer.scala
+++ b/sigmastate/src/main/scala/sigmastate/serialization/transformers/SigmaTransformerSerializer.scala
@@ -19,6 +19,9 @@ case class SigmaTransformerSerializer[I <: SigmaPropValue, O <: SigmaPropValue]
 
   override def parse(r: SigmaByteReader): SigmaPropValue = {
     val itemsSize = r.getUIntExact
+    // NO-FORK: in v5.x getUIntExact may throw Int overflow exception
+    // in v4.x r.getUInt().toInt is used and may return negative Int instead of the overflow
+    // in which case the array allocation will throw NegativeArraySizeException
     val res = safeNewArray[SigmaPropValue](itemsSize)
     cfor(0)(_ < itemsSize, _ + 1) { i =>
       res(i) = r.getValue().asInstanceOf[SigmaPropValue]
diff --git a/sigmastate/src/test/scala/org/ergoplatform/ErgoLikeTransactionSpec.scala b/sigmastate/src/test/scala/org/ergoplatform/ErgoLikeTransactionSpec.scala
index 894010b454..ab27179bec 100644
--- a/sigmastate/src/test/scala/org/ergoplatform/ErgoLikeTransactionSpec.scala
+++ b/sigmastate/src/test/scala/org/ergoplatform/ErgoLikeTransactionSpec.scala
@@ -3,11 +3,12 @@ package org.ergoplatform
 import org.ergoplatform.ErgoBox.TokenId
 import org.ergoplatform.settings.ErgoAlgos
 import scorex.crypto.hash.Digest32
+import scorex.util.encode.Base16
 import scorex.util.{Random, ModifierId}
 import sigmastate.SCollection.SByteArray
-import sigmastate.{SSigmaProp, SPair, SInt, TrivialProp, SType}
+import sigmastate.{SSigmaProp, TrivialProp, SType, SPair, SInt}
 import sigmastate.Values._
-import sigmastate.interpreter.{ProverResult, ContextExtension}
+import sigmastate.interpreter.{ContextExtension, ProverResult}
 import sigmastate.serialization.SigmaSerializer
 import sigmastate.eval._
 import sigmastate.eval.Extensions._
@@ -300,4 +301,12 @@ class ErgoLikeTransactionSpec extends SigmaDslTesting {
       }
     }
   }
+
+  property("Tuple in register test vector") {
+    val txId = "b5fd96c9f8c1ff436d609a225a12377c6873b890a145fc05f4099845b89315e5"
+    val txHex = "0278c93ee55eec066ec06290524dc01773440fbaff644bd181ab4334f97083863738644bf834de150b9abd077cf52ecb4892536ab6ad6ef8505fb932d9ca7b9fb211fc8294618723eb4909d4553f4d419762332f68865b1d703d00faae81c0e57683108c55647c5837a4fedfb52ffde04db74a8b4b77e37ab81afc3828c904862db6134e0f859ff5f62e4a5cb9da6b15ea1cd1a11dc932899d7b99e9073034ccd4e7c54fa9790d8ee356dce22ee151b044561c96000000038094ebdc031007040205c80105c8010500040004000e1f3faf2cb329f2e90d6d23b58d91bbb6c046aa143261cc21f52fbe2824bfcbf0d807d601e4c6a70408d602b2a5730000d603e4c6a70601d604e4c6a70856d605e4c6a70505d606e4c6a70705d60795720399c1a7c1720299c17202c1a7eb027201d1ededededededededed93c27202c2a793e4c672020408720193e4c6720205059572039d9c72057e8c7204010573019d9c72057e8c72040205730294e4c672020601720393e4c672020705720693e4c672020856720493e4c67202090ec5a7929c720672057207917207730395ef720393b1db630872027304d801d608b2db63087202730500ed938c7208017306938c7208027206d18f34000508cd030c8f9c4dc08f3c006fa85a47c9156dedbede000a8b764c6e374fd097e873ba0405dceeaa0401010564860202660263c0edcea7090008cd030c8f9c4dc08f3c006fa85a47c9156dedbede000a8b764c6e374fd097e873ba04d18f340000c0843d1005040004000e36100204a00b08cd0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798ea02d192a39a8cc7a701730073011001020402d19683030193a38cc7b2a57300000193c2b2a57301007473027303830108cdeeac93b1a57304d18f340000"
+    val txBytes = Base16.decode(txHex).get
+    val tx = ErgoLikeTransactionSerializer.fromBytes(txBytes)
+    tx.id shouldBe txId
+  }
 }
diff --git a/sigmastate/src/test/scala/sigmastate/helpers/NegativeTesting.scala b/sigmastate/src/test/scala/sigmastate/helpers/NegativeTesting.scala
index 60668c8c81..66875d878c 100644
--- a/sigmastate/src/test/scala/sigmastate/helpers/NegativeTesting.scala
+++ b/sigmastate/src/test/scala/sigmastate/helpers/NegativeTesting.scala
@@ -50,7 +50,7 @@ trait NegativeTesting extends Matchers {
     */
   def exceptionLike[E <: Throwable : ClassTag]
       (msgParts: String*): Throwable => Boolean = {
-    case t: E => msgParts.forall(t.getMessage.contains(_))
+    case t: E => msgParts.forall(part => t.getMessage != null && t.getMessage.contains(part))
     case _ => false
   }
 
diff --git a/sigmastate/src/test/scala/sigmastate/serialization/DeserializationResilience.scala b/sigmastate/src/test/scala/sigmastate/serialization/DeserializationResilience.scala
index 9ae7d01ab8..0ee994e413 100644
--- a/sigmastate/src/test/scala/sigmastate/serialization/DeserializationResilience.scala
+++ b/sigmastate/src/test/scala/sigmastate/serialization/DeserializationResilience.scala
@@ -6,20 +6,25 @@ import org.ergoplatform.validation.ValidationRules.CheckPositionLimit
 import org.ergoplatform.{ErgoBoxCandidate, Outputs}
 import org.scalacheck.Gen
 import scalan.util.BenchmarkUtil
+import scorex.crypto.authds.{ADKey, ADValue}
+import scorex.crypto.authds.avltree.batch.{BatchAVLProver, Insert}
+import scorex.crypto.hash.{Blake2b256, Digest32}
 import scorex.util.serialization.{Reader, VLQByteBufferReader}
-import sigmastate.Values.{BlockValue, GetVarInt, IntConstant, SValue, SigmaBoolean, SigmaPropValue, Tuple, ValDef, ValUse}
+import sigmastate.Values.{SValue, BlockValue, GetVarInt, SigmaBoolean, ValDef, ValUse, SigmaPropValue, Tuple, IntConstant}
 import sigmastate._
 import sigmastate.eval.Extensions._
 import sigmastate.eval._
-import sigmastate.helpers.{ErgoLikeContextTesting, ErgoLikeTestInterpreter, SigmaTestingCommons}
-import sigmastate.interpreter.{ContextExtension, CostedProverResult, CryptoConstants}
-import sigmastate.lang.exceptions.{DeserializeCallDepthExceeded, InvalidTypePrefix, ReaderPositionLimitExceeded, SerializerException}
+import sigmastate.helpers.{ErgoLikeTestInterpreter, SigmaTestingCommons, ErgoLikeContextTesting}
+import sigmastate.interpreter.{CryptoConstants, CostedProverResult, ContextExtension}
+import sigmastate.lang.exceptions.{ReaderPositionLimitExceeded, InvalidTypePrefix, DeserializeCallDepthExceeded, SerializerException}
 import sigmastate.serialization.OpCodes._
+import sigmastate.util.safeNewArray
 import sigmastate.utils.SigmaByteReader
 import sigmastate.utxo.SizeOf
 import sigmastate.utils.Helpers._
 
 import scala.collection.mutable
+import scala.util.{Try, Success, Failure}
 
 class DeserializationResilience extends SerializationSpecification
   with SigmaTestingCommons with CrossVersionProps {
@@ -308,5 +313,101 @@ class DeserializationResilience extends SerializationSpecification
     })
   }
 
+  /** Because this method is called from many places it should always be called with `hint`. */
+  protected def checkResult[B](res: Try[B], expectedRes: Try[B], hint: String): Unit = {
+    (res, expectedRes) match {
+      case (Failure(exception), Failure(expectedException)) =>
+        withClue(hint) {
+          rootCause(exception).getClass shouldBe rootCause(expectedException).getClass
+        }
+      case _ =>
+        val actual = rootCause(res)
+        if (actual != expectedRes) {
+          assert(false, s"$hint\nActual: $actual;\nExpected: $expectedRes\n")
+        }
+    }
+  }
+
+  def writeUInt(x: Long): Array[Byte] = {
+    val w = SigmaSerializer.startWriter()
+    val bytes = w.putUInt(x).toBytes
+    bytes
+  }
+
+  def readToInt(bytes: Array[Byte]): Try[Int] = Try {
+    val r = SigmaSerializer.startReader(bytes)
+    r.getUInt().toInt
+  }
+
+  def readToIntExact(bytes: Array[Byte]): Try[Int] = Try {
+    val r = SigmaSerializer.startReader(bytes)
+    r.getUIntExact
+  }
+
+  property("getUIntExact vs getUInt().toInt") {
+    val intOverflow = Failure(new ArithmeticException("Int overflow"))
+    val cases = Table(("stored", "toInt", "toIntExact"),
+      (0L, Success(0), Success(0)),
+      (Int.MaxValue.toLong - 1, Success(Int.MaxValue - 1), Success(Int.MaxValue - 1)),
+      (Int.MaxValue.toLong,     Success(Int.MaxValue), Success(Int.MaxValue)),
+      (Int.MaxValue.toLong + 1, Success(Int.MinValue), intOverflow),
+      (Int.MaxValue.toLong + 2, Success(Int.MinValue + 1), intOverflow),
+      (0xFFFFFFFFL,             Success(-1), intOverflow)
+    )
+    forAll(cases) { (x, res, resExact) =>
+      val bytes = writeUInt(x)
+      checkResult(readToInt(bytes), res, "toInt")
+      checkResult(readToIntExact(bytes), resExact, "toIntExact")
+    }
 
+    // check it is impossible to write negative value with reference implementation of serializer
+    // ALSO NOTE that VLQ encoded bytes are always interpreted as positive Long
+    // so the difference between getUIntExact vs getUInt().toInt boils down to how Int.MaxValue
+    // overflow is handled
+    assertExceptionThrown(
+      writeUInt(-1L),
+      exceptionLike[IllegalArgumentException]("-1 is out of unsigned int range")
+    )
+
+    val MaxUIntPlusOne = 0xFFFFFFFFL + 1
+    assertExceptionThrown(
+      writeUInt(MaxUIntPlusOne),
+      exceptionLike[IllegalArgumentException](s"$MaxUIntPlusOne is out of unsigned int range")
+    )
+  }
+
+  property("test assumptions of how negative value from getUInt().toInt is handled") {
+    assertExceptionThrown(
+      safeNewArray[Int](-1),
+      exceptionLike[NegativeArraySizeException]())
+
+    val bytes = writeUInt(10)
+    val store = new ConstantStore(IndexedSeq(IntConstant(1)))
+
+    val r = SigmaSerializer.startReader(bytes, store, true)
+    assertExceptionThrown(
+      r.constantStore.get(-1),
+      exceptionLike[ArrayIndexOutOfBoundsException]())
+
+    assertExceptionThrown(
+      r.getBytes(-1),
+      exceptionLike[NegativeArraySizeException]())
+
+    r.valDefTypeStore(-1) = SInt // no exception on negative key
+
+    // the following example shows how far negative keyLength can go inside AvlTree operations
+    val avlProver = new BatchAVLProver[Digest32, Blake2b256.type](keyLength = 32, None)
+    val digest = avlProver.digest
+    val flags = AvlTreeFlags(true, false, false)
+    val treeData = new AvlTreeData(digest, flags, -1, None)
+    val tree = SigmaDsl.avlTree(treeData)
+    val k = Blake2b256.hash("1")
+    val v = k
+    avlProver.performOneOperation(Insert(ADKey @@ k, ADValue @@ v))
+    val proof = avlProver.generateProof()
+    val verifier = tree.createVerifier(Colls.fromArray(proof))
+    verifier.performOneOperation(Insert(ADKey @@ k, ADValue @@ v)).isFailure shouldBe true
+    // NOTE, even though performOneOperation fails, some AvlTree$ methods used in Interpreter
+    // (remove_eval, update_eval, contains_eval) won't throw, while others will.
+  }
 }