diff --git a/Python/modsupport.c b/Python/modsupport.c
index 08f5065..428914f 100644
--- a/Python/modsupport.c
+++ b/Python/modsupport.c
@@ -148,15 +148,6 @@
     return v;
 }
 
-static int
-_ustrlen(Py_UNICODE *u)
-{
-    int i = 0;
-    Py_UNICODE *v = u;
-    while (*v != 0) { i++; v++; }
-    return i;
-}
-
 static PyObject *
 do_mktuple(const char **p_format, va_list *p_va, int endchar, int n, int flags)
 {
@@ -269,7 +260,7 @@
             }
             else {
                 if (n < 0)
-                    n = _ustrlen(u);
+                    n = Py_UNICODE_strlen(u);
                 v = PyUnicode_FromUnicode(u, n);
             }
             return v;