diff --git a/hbs2-core/lib/HBS2/Net/Proto/RefChan.hs b/hbs2-core/lib/HBS2/Net/Proto/RefChan.hs
index a68f3c46..8adf7e06 100644
--- a/hbs2-core/lib/HBS2/Net/Proto/RefChan.hs
+++ b/hbs2-core/lib/HBS2/Net/Proto/RefChan.hs
@@ -364,6 +364,8 @@ refChanUpdateProto self pc adapter msg = do
 
        let h0 = hashObject @HbSync (serialise msg)
 
+       guard =<< liftIO (hasBlock sto h0 <&> isJust)
+
        debug $ "RefChanUpdate/ACCEPT" <+> pretty h0
 
        (peerKey, AcceptTran headRef hashRef) <- MaybeT $ pure $ unboxSignedBox0 box