diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index da17bfe..1e1f257 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -40,6 +40,7 @@
 
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
+#include "pycore_abstract.h"   // _PyIndex_Check()
 #include "pycore_bytes_methods.h"
 #include "pycore_fileutils.h"
 #include "pycore_initconfig.h"
@@ -14132,7 +14133,7 @@
     if (PyUnicode_READY(self) == -1)
         return NULL;
 
-    if (PyIndex_Check(item)) {
+    if (_PyIndex_Check(item)) {
         Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
         if (i == -1 && PyErr_Occurred())
             return NULL;