diff -r 56a7721ee3ec -r 2315a95ee887 mercurial/mdiff.py
--- a/mercurial/mdiff.py	Mon Aug 23 13:24:19 2010 +0200
+++ b/mercurial/mdiff.py	Mon Aug 23 13:28:04 2010 +0200
@@ -260,6 +260,9 @@
     return "".join(t)
 
 def patch(a, bin):
+    if len(a) == 0:
+        # skip over trivial delta header
+        return buffer(bin, 12)
     return mpatch.patches(a, [bin])
 
 # similar to difflib.SequenceMatcher.get_matching_blocks