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
@@ -1202,7 +1202,8 @@
 	CHN_FOREACH(c, d, channels.pcm) {
 		if (c->type != type)
 			continue;
-		unit++;
+		while (c->unit == unit)
+			unit++;
 	}
 
 	PCM_UNLOCK(d);