--- a/hgext3rd/topic/discovery.py	Thu Apr 18 13:01:39 2019 +0200
+++ b/hgext3rd/topic/discovery.py	Thu Apr 18 13:02:06 2019 +0200
@@ -123,6 +123,8 @@
             remote.branchmap = origremotebranchmap
 
 def wireprotobranchmap(orig, repo, proto):
+    if not common.hastopicext(repo):
+        return orig(repo, proto)
     oldrepo = repo.__class__
     try:
         class repocls(repo.__class__):