diff -r da5a666f0f78 -r 6104b203bec8 mercurial/pure/parsers.py
--- a/mercurial/pure/parsers.py	Fri Jul 20 14:25:59 2018 -0700
+++ b/mercurial/pure/parsers.py	Wed Aug 01 10:57:14 2018 -0700
@@ -41,8 +41,7 @@
     def __len__(self):
         return self._lgt + len(self._extra) + 1
 
-    def insert(self, i, tup):
-        assert i == -1
+    def append(self, tup):
         self._extra.append(tup)
 
     def _fix_index(self, i):