diff -r 4f885770c4a2 -r 00368bc0a614 mercurial/crecord.py
--- a/mercurial/crecord.py	Tue Jun 19 13:49:06 2018 -0700
+++ b/mercurial/crecord.py	Thu Jun 21 09:32:31 2018 -0700
@@ -403,7 +403,7 @@
         if fromline != 0:
             if fromlen == 0:
                 fromline -= 1
-            if tolen == 0:
+            if tolen == 0 and toline > 0:
                 toline -= 1
 
         fromtoline = '@@ -%d,%d +%d,%d @@%s\n' % (