diff --git a/Include/listobject.h b/Include/listobject.h
index 76cf86d..5ff057e 100644
--- a/Include/listobject.h
+++ b/Include/listobject.h
@@ -24,3 +24,4 @@
 extern int setlistitem PROTO((object *, int, object *));
 extern int inslistitem PROTO((object *, int, object *));
 extern int addlistitem PROTO((object *, object *));
+extern int sortlist PROTO((object *));