diff --git a/Python/pystate.c b/Python/pystate.c
index 31b5423..1392331 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -248,7 +248,7 @@
         return NULL;
     if (state->modules_by_index == NULL)
         return NULL;
-    if (index > PyList_GET_SIZE(state->modules_by_index))
+    if (index >= PyList_GET_SIZE(state->modules_by_index))
         return NULL;
     res = PyList_GET_ITEM(state->modules_by_index, index);
     return res==Py_None ? NULL : res;