diff --git a/doc/syntax.rst b/doc/syntax.rst
index a6383bd6..fb38a5c8 100644
--- a/doc/syntax.rst
+++ b/doc/syntax.rst
@@ -31,7 +31,7 @@ by a colon ``':'``.  These specify a non-default format for the replacement valu
 
 See also the :ref:`formatspec` section.
 
-If the numerical arg_indexes in a format string are 0, 1, 2, ... in sequence,
+If the numerical arg_ids in a format string are 0, 1, 2, ... in sequence,
 they can all be omitted (not just some) and the numbers 0, 1, 2, ... will be
 automatically inserted in that order.