Index: Python/_warnings.c
===================================================================
--- Python/_warnings.c  (revision 65930)
+++ Python/_warnings.c  (working copy)
@@ -388,7 +388,7 @@
         else {
             const char *msg = "functions overriding warnings.showwarning() "
                                 "must support the 'line' argument";
-            const char *text_char = _PyUnicode_AsString(text);
+            const char *text_char = _PyUnicode_AsString(PyObject_Str(text));

             if (strcmp(msg, text_char) == 0) {
                 /* Prevent infinite recursion by using built-in implementation