diff --git a/cmd/sound.c b/cmd/sound.c
index f82f2aa..20ac3f7 100644
--- a/cmd/sound.c
+++ b/cmd/sound.c
@@ -86,5 +86,5 @@
 	sound, 4, 1, do_sound,
 	"sound sub-system",
 	"init - initialise the sound driver\n"
-	"sound play [len] [freq] - play a sound for len ms at freq hz\n"
+	"sound play [len [freq]] - play a sound for len ms at freq Hz\n"
 );