diff -r 9d457bb38de5 -r 5185a24ce04e mercurial/util.py
--- a/mercurial/util.py	Sat Dec 06 15:40:04 2008 +0100
+++ b/mercurial/util.py	Sat Dec 06 15:53:57 2008 +0100
@@ -705,7 +705,7 @@
         if cwd is not None and oldcwd != cwd:
             os.chdir(oldcwd)
 
-class SignatureError:
+class SignatureError(Exception):
     pass
 
 def checksignature(func):