diff --git a/Include/complexobject.h b/Include/complexobject.h
index c379b08..3e4ecff 100644
--- a/Include/complexobject.h
+++ b/Include/complexobject.h
@@ -64,8 +64,9 @@
    (Advanced String Formatting). */
 #ifndef Py_LIMITED_API
 PyAPI_FUNC(PyObject *) _PyComplex_FormatAdvanced(PyObject *obj,
-                                                 Py_UNICODE *format_spec,
-                                                 Py_ssize_t format_spec_len);
+                                                 PyObject *format_spec,
+                                                 Py_ssize_t start,
+                                                 Py_ssize_t end);
 #endif
 
 #ifdef __cplusplus