diff -r 1bb465fad209 -r 62855e1ce9d8 hgext3rd/topic/revset.py
--- a/hgext3rd/topic/revset.py	Wed Apr 08 01:16:57 2020 +0800
+++ b/hgext3rd/topic/revset.py	Fri May 08 20:36:32 2020 +0800
@@ -124,6 +124,7 @@
                 b'relation subscript bounds must be integers',
                 None, None)
         else:
+            # hg <= 4.9 (431cf2c8c839+13f7a6a4f0db)
             a = b = z
 
         s = revset.getset(repo, revset.fullreposet(repo), x)
@@ -164,7 +165,10 @@
 
     def topicrel(repo, subset, x, *args):
         subset &= topicset(repo, subset, x)
-        return revset.generationsrel(repo, subset, x, *args)
+        # not using revset.generationssubrel directly because it was renamed
+        # hg <= 5.3 (8859de3e83dc)
+        generationssubrel = revset.subscriptrelations[b'generations']
+        return generationssubrel(repo, subset, x, *args)
 
     revset.subscriptrelations[b'topic'] = topicrel
     revset.subscriptrelations[b't'] = topicrel