diff --git a/sys/dev/sound/pcm/channel.c b/sys/dev/sound/pcm/channel.c
--- a/sys/dev/sound/pcm/channel.c
+++ b/sys/dev/sound/pcm/channel.c
@@ -332,6 +332,8 @@
 	int ret;
 
 	CHN_LOCKASSERT(c);
+	KASSERT((c->flags & CHN_F_SLEEPING) == 0,
+	    ("%s(): entered with CHN_F_SLEEPING", __func__));
 
 	if (c->flags & CHN_F_DEAD)
 		return (EINVAL);