diff --git a/src/proto/sound.pro b/src/proto/sound.pro
index cf8439a..ad1c2b5 100644
--- a/src/proto/sound.pro
+++ b/src/proto/sound.pro
@@ -1,4 +1,7 @@
 /* sound.c */
+int has_any_sound_callback(void);
+int has_sound_callback_in_queue(void);
+void invoke_sound_callback(void);
 void f_sound_playevent(typval_T *argvars, typval_T *rettv);
 void f_sound_playfile(typval_T *argvars, typval_T *rettv);
 void f_sound_stop(typval_T *argvars, typval_T *rettv);