diff --git a/hbs2-core/lib/HBS2/Storage/Operations/ByteString.hs b/hbs2-core/lib/HBS2/Storage/Operations/ByteString.hs
index 88ec467a..d9affee4 100644
--- a/hbs2-core/lib/HBS2/Storage/Operations/ByteString.hs
+++ b/hbs2-core/lib/HBS2/Storage/Operations/ByteString.hs
@@ -37,6 +37,8 @@ instance Exception WriteMerkleIOError
 
 instance (MonadIO m, h ~ HbSync, Storage s h ByteString m) => MerkleWriter ByteString h s m where
   type instance ToBlockW ByteString = ByteString
+
+  -- FIXME: concurrent-enqueue
   writeAsMerkle sto bs = do
 
     hashes <- do
diff --git a/hbs2-storage-ncq/lib/HBS2/Storage/NCQ3/Internal/Class.hs b/hbs2-storage-ncq/lib/HBS2/Storage/NCQ3/Internal/Class.hs
index f461377e..280a4a6e 100644
--- a/hbs2-storage-ncq/lib/HBS2/Storage/NCQ3/Internal/Class.hs
+++ b/hbs2-storage-ncq/lib/HBS2/Storage/NCQ3/Internal/Class.hs
@@ -22,7 +22,7 @@ instance MonadUnliftIO m => Storage NCQStorage HbSync LBS.ByteString m where
 
   putBlock     sto lbs = fmap coerce <$> ncqPutBlock sto lbs
 
-  enqueueBlock sto lbs = fmap coerce <$> ncqPutBlock sto lbs
+  enqueueBlock sto lbs = fmap coerce <$> ncqTossBlock sto lbs
 
   getBlock sto h = runMaybeT $ do
     bs <- MaybeT (ncqStorageGetBlock sto (coerce h))