diff --git a/hbs2-core/lib/HBS2/Net/Proto/RefChan.hs b/hbs2-core/lib/HBS2/Net/Proto/RefChan.hs
index 0585fd7f..2212f9aa 100644
--- a/hbs2-core/lib/HBS2/Net/Proto/RefChan.hs
+++ b/hbs2-core/lib/HBS2/Net/Proto/RefChan.hs
@@ -301,6 +301,10 @@ refChanUpdateProto self pc adapter msg = do
 
        let h0 = hashObject @HbSync (serialise msg)
 
+       done <- liftIO (hasBlock sto h0) <&> isJust
+
+       guard (not done)
+
        debug $ "RefChanUpdate/Propose" <+> pretty h0
 
        deferred proto do