--- a/mercurial/pure/parsers.py	Thu Dec 16 17:34:51 2021 +0100
+++ b/mercurial/pure/parsers.py	Wed Dec 15 15:28:30 2021 +0100
@@ -647,7 +647,7 @@
         if not isinstance(i, int):
             raise TypeError(b"expecting int indexes")
         if i < 0 or i >= len(self):
-            raise IndexError
+            raise IndexError(i)
 
     def __getitem__(self, i):
         if i == -1: