diff -r 5c153c69fdb2 -r c5df4af17110 mercurial/help.py
--- a/mercurial/help.py	Tue Aug 26 04:58:41 2014 -0700
+++ b/mercurial/help.py	Thu Sep 04 09:59:23 2014 -0400
@@ -87,9 +87,10 @@
                'extensioncommands': [],
                }
     for names, header, doc in helptable:
+        # Old extensions may use a str as doc.
         if (sum(map(lowercontains, names))
             or lowercontains(header)
-            or lowercontains(doc())):
+            or (callable(doc) and lowercontains(doc()))):
             results['topics'].append((names[0], header))
     import commands # avoid cycle
     for cmd, entry in commands.table.iteritems():