--- a/mercurial/commands.py	Tue Jul 13 22:56:01 2010 +0900
+++ b/mercurial/commands.py	Tue Jul 13 17:30:29 2010 +0200
@@ -83,7 +83,7 @@
     Returns 0 if all files are successfully added.
     """
     try:
-        sim = float(opts.get('similarity') or 0)
+        sim = float(opts.get('similarity') or 100)
     except ValueError:
         raise util.Abort(_('similarity must be a number'))
     if sim < 0 or sim > 100: