diff --git a/Modules/threadmodule.c b/Modules/threadmodule.c
index baf6673..61ad5d3 100644
--- a/Modules/threadmodule.c
+++ b/Modules/threadmodule.c
@@ -191,7 +191,7 @@
 	Py_XINCREF(kw);
 	self->kw = kw;
 	self->dict = NULL;	/* making sure */
-	self->key = PyString_FromFormat("thread.local.%p", self);
+	self->key = PyUnicode_FromFormat("thread.local.%p", self);
 	if (self->key == NULL) 
 		goto err;