--- a/mercurial/hg.py	Sun Jul 10 10:06:54 2005 -0800
+++ b/mercurial/hg.py	Sun Jul 10 10:38:50 2005 -0800
@@ -608,7 +608,10 @@
         try:
             return self.tags()[key]
         except KeyError:
-            return self.changelog.lookup(key)
+            try:
+                return self.changelog.lookup(key)
+            except:
+                raise RepoError("unknown revision '%s'" % key)
 
     def dev(self):
         if self.remote: return -1