diff --git a/src/proto/os_mswin.pro b/src/proto/os_mswin.pro
index 333ba76..fb2da93 100644
--- a/src/proto/os_mswin.pro
+++ b/src/proto/os_mswin.pro
@@ -49,6 +49,7 @@
 char_u *serverGetReply(HWND server, int *expr_res, int remove, int wait);
 void serverProcessPendingMessages(void);
 char *charset_id2name(int id);
+char *quality_id2name __ARGS((DWORD id));
 int get_logfont(LOGFONT *lf, char_u *name, HDC printer_dc, int verbose);
 void channel_init_winsock(void);
 /* vim: set ft=c : */