--- a/mercurial/repair.py	Fri Jan 06 09:56:40 2017 +0800
+++ b/mercurial/repair.py	Wed Jan 04 10:07:12 2017 -0800
@@ -99,9 +99,9 @@
     # (head = revision in the set that has no descendant in the set;
     #  base = revision in the set that has no ancestor in the set)
     tostrip = set(striplist)
-    for rev in striplist:
-        for desc in cl.descendants([rev]):
-            tostrip.add(desc)
+    for r in cl.revs(start=striprev + 1):
+        if any(p in tostrip for p in cl.parentrevs(r)):
+            tostrip.add(r)
 
     files = _collectfiles(repo, striprev)
     saverevs = _collectbrokencsets(repo, files, striprev)