hgext/mq.py

--- a/hgext/mq.py	Mon Dec 19 23:31:38 2011 +0100
+++ b/hgext/mq.py	Wed Dec 21 23:47:18 2011 +0100
@@ -1765,6 +1765,9 @@
 
             diffopts = self.diffopts({'git': git})
             for r in rev:
+                if not repo[r].mutable():
+                    raise util.Abort(_('revision %d is not mutable') % r,
+                                     hint=_('see "hg help phases" for details'))
                 p1, p2 = repo.changelog.parentrevs(r)
                 n = repo.changelog.node(r)
                 if p2 != nullrev: