--- a/mercurial/pure/parsers.py	Fri Jul 20 22:26:28 2018 -0700
+++ b/mercurial/pure/parsers.py	Fri Jul 20 09:53:54 2018 -0700
@@ -55,9 +55,9 @@
         return i
 
     def __getitem__(self, i):
+        if i == -1 or i == len(self) - 1:
+            return (0, 0, 0, -1, -1, -1, -1, nullid)
         i = self._fix_index(i)
-        if i == len(self) - 1:
-            return (0, 0, 0, -1, -1, -1, -1, nullid)
         if i >= self._lgt:
             return self._extra[i - self._lgt]
         index = self._calculate_index(i)