diff --git a/sys/dev/sound/pcm/sound.c b/sys/dev/sound/pcm/sound.c
--- a/sys/dev/sound/pcm/sound.c
+++ b/sys/dev/sound/pcm/sound.c
@@ -1325,7 +1325,8 @@
 		CHN_FOREACH(c, d, channels.pcm) {
 			CHN_UNLOCKASSERT(c);
 			CHN_LOCK(c);
-			if (c->flags & CHN_F_BUSY)
+			if (c->flags & CHN_F_BUSY &&
+			    j < (int)(nitems(si->openedaudio) * intnbits))
 				si->openedaudio[j / intnbits] |=
 				    (1 << (j % intnbits));
 			CHN_UNLOCK(c);