--- a/hgext/extdiff.py	Wed Mar 16 16:07:06 2011 +0100
+++ b/hgext/extdiff.py	Tue Mar 15 17:50:02 2011 -0400
@@ -121,7 +121,7 @@
         msg = _('cannot specify --rev and --change at the same time')
         raise util.Abort(msg)
     elif change:
-        node2 = repo.lookup(change)
+        node2 = cmdutil.revsingle(repo, change, None).node()
         node1a, node1b = repo.changelog.parents(node2)
     else:
         node1a, node2 = cmdutil.revpair(repo, revs)

--- a/tests/test-extdiff.t	Wed Mar 16 16:07:06 2011 +0100
+++ b/tests/test-extdiff.t	Tue Mar 15 17:50:02 2011 -0400
@@ -168,3 +168,12 @@
   diffing this a.8a5febb7f867/a a.34eed99112ab/a
   [1]
 
+Test with revsets:
+
+  $ hg extdif -p echo -c "rev(1)"
+  a.8a5febb7f867/a a.34eed99112ab/a
+  [1]
+
+  $ hg extdif -p echo -r "0::1"
+  a.8a5febb7f867/a a.34eed99112ab/a
+  [1]