diff -r 1f510efcd5f3 -r f8b5c3e77d4b mercurial/patch.py
--- a/mercurial/patch.py	Wed Nov 12 23:29:14 2014 -0800
+++ b/mercurial/patch.py	Wed Nov 12 23:50:21 2014 -0800
@@ -1738,9 +1738,15 @@
         s.update(text)
         return s.hexdigest()
 
+    if opts.noprefix:
+        aprefix = bprefix = ''
+    else:
+        aprefix = 'a/'
+        bprefix = 'b/'
+
     def diffline(a, b, revs):
         if opts.git:
-            line = 'diff --git a/%s b/%s\n' % (a, b)
+            line = 'diff --git %s%s %s%s\n' % (aprefix, a, bprefix, b)
         elif not repo.ui.quiet:
             if revs:
                 revinfo = ' '.join(["-r %s" % rev for rev in revs])