diff --git a/Objects/stringlib/stringdefs.h b/Objects/stringlib/stringdefs.h
index 1659315..a5672c7 100644
--- a/Objects/stringlib/stringdefs.h
+++ b/Objects/stringlib/stringdefs.h
@@ -13,8 +13,8 @@
 #define STRINGLIB_EMPTY          nullstring
 #define STRINGLIB_ISDECIMAL(x)   ((x >= '0') && (x <= '9'))
 #define STRINGLIB_TODECIMAL(x)   (STRINGLIB_ISDECIMAL(x) ? (x - '0') : -1)
-#define STRINGLIB_TOUPPER        toupper
-#define STRINGLIB_TOLOWER        tolower
+#define STRINGLIB_TOUPPER        Py_TOUPPER
+#define STRINGLIB_TOLOWER        Py_TOLOWER
 #define STRINGLIB_FILL           memset
 #define STRINGLIB_STR            PyBytes_AS_STRING
 #define STRINGLIB_LEN            PyBytes_GET_SIZE