diff --git a/blockdag/dagio.go b/blockdag/dagio.go
index 05698cf5c..4ad53a6a2 100644
--- a/blockdag/dagio.go
+++ b/blockdag/dagio.go
@@ -699,7 +699,7 @@ func dbStoreBlockNode(dbTx database.Tx, node *blockNode) error {
 
 	// Write block header data to block index bucket.
 	blockIndexBucket := dbTx.Metadata().Bucket(blockIndexBucketName)
-	key := blockIndexKey(node.hash)
+	key := blockIndexKey(node.hash, node.blueScore)
 	return blockIndexBucket.Put(key, value)
 }
 
@@ -717,10 +717,13 @@ func dbStoreBlock(dbTx database.Tx, block *util.Block) error {
 }
 
 // blockIndexKey generates the binary key for an entry in the block index
-// bucket. The key is composed only of the 32 byte block hash.
-func blockIndexKey(blockHash *daghash.Hash) []byte {
-	indexKey := make([]byte, daghash.HashSize)
-	copy(indexKey[:], blockHash[:])
+// bucket. The key is composed of the block blue score encoded as a big-endian
+// 64-bit unsigned int followed by the 32 byte block hash.
+// The blue score component is important for iteration order.
+func blockIndexKey(blockHash *daghash.Hash, blueScore uint64) []byte {
+	indexKey := make([]byte, daghash.HashSize+8)
+	binary.BigEndian.PutUint64(indexKey[0:8], blueScore)
+	copy(indexKey[8:daghash.HashSize+8], blockHash[:])
 	return indexKey
 }