diff --git a/core/block_validator.go b/core/block_validator.go
index 45a2957900..1da22f84ab 100644
--- a/core/block_validator.go
+++ b/core/block_validator.go
@@ -226,6 +226,9 @@ func (v *BlockValidator) ValidateL1Messages(block *types.Block) error {
 		// TODO: consider verifying that skipped messages overflow
 		for index := queueIndex; index < txQueueIndex; index++ {
 			if exists := it.Next(); !exists {
+				if err := it.Error(); err != nil {
+					log.Error("Unexpected DB error in ValidateL1Messages", "err", err, "queueIndex", queueIndex)
+				}
 				// the message in this block is not available in our local db.
 				// we'll reprocess this block at a later time.
 				return consensus.ErrMissingL1MessageData
@@ -240,6 +243,9 @@ func (v *BlockValidator) ValidateL1Messages(block *types.Block) error {
 		queueIndex = txQueueIndex + 1
 
 		if exists := it.Next(); !exists {
+			if err := it.Error(); err != nil {
+				log.Error("Unexpected DB error in ValidateL1Messages", "err", err, "queueIndex", txQueueIndex)
+			}
 			// the message in this block is not available in our local db.
 			// we'll reprocess this block at a later time.
 			return consensus.ErrMissingL1MessageData
diff --git a/core/rawdb/accessors_l1_message.go b/core/rawdb/accessors_l1_message.go
index b425f47344..f7aab15444 100644
--- a/core/rawdb/accessors_l1_message.go
+++ b/core/rawdb/accessors_l1_message.go
@@ -202,6 +202,12 @@ func (it *L1MessageIterator) Release() {
 	it.inner.Release()
 }
 
+// Error returns any accumulated error.
+// Exhausting all the key/value pairs is not considered to be an error.
+func (it *L1MessageIterator) Error() error {
+	return it.inner.Error()
+}
+
 // ReadL1MessagesFrom retrieves up to `maxCount` L1 messages starting at `startIndex`.
 func ReadL1MessagesFrom(db ethdb.Database, startIndex, maxCount uint64) []types.L1MessageTx {
 	msgs := make([]types.L1MessageTx, 0, maxCount)
@@ -236,6 +242,10 @@ func ReadL1MessagesFrom(db ethdb.Database, startIndex, maxCount uint64) []types.
 		}
 	}
 
+	if err := it.Error(); err != nil {
+		log.Crit("Failed to read L1 messages", "err", err)
+	}
+
 	return msgs
 }
 
diff --git a/rollup/sync_service/bridge_client.go b/rollup/sync_service/bridge_client.go
index 47b12ac2f2..200b16bbb7 100644
--- a/rollup/sync_service/bridge_client.go
+++ b/rollup/sync_service/bridge_client.go
@@ -86,6 +86,10 @@ func (c *BridgeClient) fetchMessagesInRange(ctx context.Context, from, to uint64
 		})
 	}
 
+	if err := it.Error(); err != nil {
+		return nil, err
+	}
+
 	return msgs, nil
 }
 
diff --git a/rollup/sync_service/sync_service.go b/rollup/sync_service/sync_service.go
index c5d3cf3780..ad5a6b0001 100644
--- a/rollup/sync_service/sync_service.go
+++ b/rollup/sync_service/sync_service.go
@@ -149,6 +149,9 @@ func (s *SyncService) fetchMessages() {
 
 	log.Trace("Sync service fetchMessages", "latestProcessedBlock", s.latestProcessedBlock, "latestConfirmed", latestConfirmed)
 
+	// keep track of next queue index we're expecting to see
+	queueIndex := rawdb.ReadHighestSyncedQueueIndex(s.db)
+
 	batchWriter := s.db.NewBatch()
 	numBlocksPendingDbWrite := uint64(0)
 	numMessagesPendingDbWrite := 0
@@ -216,7 +219,18 @@ func (s *SyncService) fetchMessages() {
 			numMsgsCollected += len(msgs)
 		}
 
-		numBlocksPendingDbWrite += to - from
+		for _, msg := range msgs {
+			if msg.QueueIndex > 0 {
+				queueIndex++
+			}
+			// check if received queue index matches expected queue index
+			if msg.QueueIndex != queueIndex {
+				log.Error("Unexpected queue index in SyncService", "expected", queueIndex, "got", msg.QueueIndex, "msg", msg)
+				return // do not flush inconsistent data to disk
+			}
+		}
+
+		numBlocksPendingDbWrite += to - from + 1
 		numMessagesPendingDbWrite += len(msgs)
 
 		// flush new messages to database periodically