--- a/mercurial/patch.py	Thu Dec 17 22:29:41 2015 +0900
+++ b/mercurial/patch.py	Thu Dec 17 11:00:06 2015 -0800
@@ -2146,7 +2146,7 @@
                                             'ignoreblanklines')
     if formatchanging:
         buildopts['text'] = opts and opts.get('text')
-        buildopts['nobinary'] = get('nobinary')
+        buildopts['nobinary'] = get('nobinary', forceplain=False)
         buildopts['noprefix'] = get('noprefix', forceplain=False)
 
     return mdiff.diffopts(**buildopts)