diff -r 55c6788c54e2 -r a8e55d6f1d67 mercurial/revlog.py
--- a/mercurial/revlog.py	Tue Mar 21 22:47:49 2017 -0700
+++ b/mercurial/revlog.py	Tue Mar 21 17:39:49 2017 -0400
@@ -33,6 +33,7 @@
     error,
     mdiff,
     parsers,
+    pycompat,
     templatefilters,
     util,
 )
@@ -943,7 +944,7 @@
             ancs = self.index.commonancestorsheads(a, b)
         except (AttributeError, OverflowError): # C implementation failed
             ancs = ancestor.commonancestorsheads(self.parentrevs, a, b)
-        return map(self.node, ancs)
+        return pycompat.maplist(self.node, ancs)
 
     def isancestor(self, a, b):
         """return True if node a is an ancestor of node b