--- a/mercurial/discovery.py	Tue May 29 23:26:55 2012 +0200
+++ b/mercurial/discovery.py	Fri Jun 01 12:37:18 2012 -0700
@@ -140,7 +140,7 @@
         og._computecommonmissing()
         cl = repo.changelog
         missingrevs = set(cl.rev(n) for n in og._missing)
-        og._common = set(cl.ancestors(*missingrevs)) - missingrevs
+        og._common = set(cl.ancestors(missingrevs)) - missingrevs
         commonheads = set(og.commonheads)
         og.missingheads = [h for h in og.missingheads if h not in commonheads]