diff -r bfb38c5cebf4 -r 6e6452bc441d mercurial/crecord.py
--- a/mercurial/crecord.py	Wed Aug 30 09:21:31 2017 -0700
+++ b/mercurial/crecord.py	Wed Aug 30 20:25:56 2017 +0000
@@ -1563,8 +1563,7 @@
 
             # start the editor and wait for it to complete
             try:
-                patch = self.ui.edit(patch.getvalue(), "",
-                                     extra={"suffix": ".diff"})
+                patch = self.ui.edit(patch.getvalue(), "", action="diff")
             except error.Abort as exc:
                 self.errorstr = str(exc)
                 return None