diff --git a/crates/batcher/src/proposal_manager.rs b/crates/batcher/src/proposal_manager.rs
index cadcc0b2c1..9b5b5369b7 100644
--- a/crates/batcher/src/proposal_manager.rs
+++ b/crates/batcher/src/proposal_manager.rs
@@ -16,7 +16,7 @@ use tokio::sync::Mutex;
 use tracing::{debug, error, info, instrument, Instrument};
 
 use crate::batcher::BatcherStorageReaderTrait;
-use crate::block_builder::{BlockBuilderError, BlockBuilderFactoryTrait, BlockExecutionArtifacts};
+use crate::block_builder::{BlockBuilderError, BlockBuilderFactoryTrait, BlockBuilderTrait, BlockExecutionArtifacts};
 use crate::transaction_provider::ProposeTransactionProvider;
 
 #[derive(Debug, Error)]
@@ -173,7 +173,7 @@ impl ProposalManagerTrait for ProposalManager {
 
         let tx_provider =
             ProposeTransactionProvider { mempool_client: self.mempool_client.clone() };
-        let mut block_builder = self.block_builder_factory.create_block_builder(
+        let block_builder = self.block_builder_factory.create_block_builder(
             height,
             retrospective_block_hash,
             deadline,
@@ -182,29 +182,7 @@ impl ProposalManagerTrait for ProposalManager {
             false,
         )?;
 
-        let active_proposal = self.active_proposal.clone();
-        let executed_proposals = self.executed_proposals.clone();
-
-        self.active_proposal_handle = Some(tokio::spawn(
-            async move {
-                let result = block_builder
-                    .build_block()
-                    .await
-                    .map(ProposalOutput::from)
-                    .map_err(|e| GetProposalResultError::BlockBuilderError(Arc::new(e)));
-
-                executed_proposals.lock().await.insert(proposal_id, result);
-
-                // The proposal is done, clear the active proposal.
-                let mut active_proposal = active_proposal.lock().await;
-                if let Some(current_active_proposal_id) = *active_proposal {
-                    if current_active_proposal_id == proposal_id {
-                        active_proposal.take();
-                    }
-                }
-            }
-            .in_current_span(),
-        ));
+        self.spawn_build_block_task(proposal_id, block_builder).await?;
 
         Ok(())
     }
@@ -268,6 +246,37 @@ impl ProposalManager {
         }
     }
 
+    async fn spawn_build_block_task(
+        &mut self,
+        proposal_id: ProposalId,
+        mut block_builder: Box<dyn BlockBuilderTrait>,
+    ) -> Result<(), BuildProposalError> {
+        let active_proposal = self.active_proposal.clone();
+        let executed_proposals = self.executed_proposals.clone();
+
+        self.active_proposal_handle = Some(tokio::spawn(
+            async move {
+                let result = block_builder
+                    .build_block()
+                    .await
+                    .map(ProposalOutput::from)
+                    .map_err(|e| GetProposalResultError::BlockBuilderError(Arc::new(e)));
+
+                executed_proposals.lock().await.insert(proposal_id, result);
+
+                // The proposal is done, clear the active proposal.
+                let mut active_proposal = active_proposal.lock().await;
+                if let Some(current_active_proposal_id) = *active_proposal {
+                    if current_active_proposal_id == proposal_id {
+                        active_proposal.take();
+                    }
+                }
+            }
+            .in_current_span(),
+        ));
+        Ok(())
+    }
+
     async fn reset_active_height(&mut self) {
         if let Some(_active_proposal) = self.active_proposal.lock().await.take() {
             // TODO: Abort the block_builder.