--- a/mercurial/scmutil.py	Wed May 16 13:45:46 2012 -0700
+++ b/mercurial/scmutil.py	Wed May 30 14:21:58 2012 -0500
@@ -525,9 +525,11 @@
     l = revrange(repo, revs)
 
     if len(l) == 0:
+        if revs:
+            raise util.Abort(_('empty revision range'))
         return repo.dirstate.p1(), None
 
-    if len(l) == 1:
+    if len(l) == 1 and len(revs) == 1 and _revrangesep not in revs[0]:
         return repo.lookup(l[0]), None
 
     return repo.lookup(l[0]), repo.lookup(l[-1])