diff --git a/src/proto/gui_w32.pro b/src/proto/gui_w32.pro
index 680a9f5..c10b9a2 100644
--- a/src/proto/gui_w32.pro
+++ b/src/proto/gui_w32.pro
@@ -88,4 +88,5 @@
 BalloonEval *gui_mch_create_beval_area __ARGS((void *target, char_u *mesg, void (*mesgCB)(BalloonEval *, int), void *clientData));
 void gui_mch_destroy_beval_area __ARGS((BalloonEval *beval));
 void netbeans_draw_multisign_indicator __ARGS((int row));
+int multiline_balloon_available __ARGS((void));
 /* vim: set ft=c : */