--- a/mercurial/revset.py	Thu Feb 26 06:03:39 2015 +0900
+++ b/mercurial/revset.py	Fri Feb 06 02:52:10 2015 +0100
@@ -527,7 +527,7 @@
     import branchmap
     urepo = repo.unfiltered()
     ucl = urepo.changelog
-    getbi = branchmap.revbranchcache(urepo).branchinfo
+    getbi = branchmap.revbranchcache(urepo, readonly=True).branchinfo
 
     try:
         b = getstring(x, '')