diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index a5ae454..949205a 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -13915,10 +13915,11 @@
         int src_kind, dest_kind;
         Py_UCS4 ch, max_char, kind_limit;
 
-        if (PySlice_GetIndicesEx(item, PyUnicode_GET_LENGTH(self),
-                                 &start, &stop, &step, &slicelength) < 0) {
+        if (PySlice_Unpack(item, &start, &stop, &step) < 0) {
             return NULL;
         }
+        slicelength = PySlice_AdjustIndices(PyUnicode_GET_LENGTH(self),
+                                            &start, &stop, step);
 
         if (slicelength <= 0) {
             _Py_RETURN_UNICODE_EMPTY();