diff --git a/src/sound.c b/src/sound.c
index f3d651e..a968ecd 100644
--- a/src/sound.c
+++ b/src/sound.c
@@ -339,7 +339,7 @@
 }
 
     static HWND
-sound_window()
+sound_window(void)
 {
     if (g_hWndSound == NULL)
     {