diff --git a/spa/plugins/alsa/acp/channelmap.h b/spa/plugins/alsa/acp/channelmap.h
index ee20801e3..9dc9b8c3d 100644
--- a/spa/plugins/alsa/acp/channelmap.h
+++ b/spa/plugins/alsa/acp/channelmap.h
@@ -194,7 +194,7 @@ static inline pa_channel_map* pa_channel_map_init_extend(pa_channel_map *m,
 		if (pa_channel_map_init_auto(m, c, def) == NULL)
 			continue;
 		for (i = 0; c < channels; c++, i++)
-			m->map[c] = PA_CHANNEL_POSITION_AUX0 + i;
+			m->map[c] = PA_CHANNEL_POSITION_AUX0 + (i & 31);
 		m->channels = (uint8_t) channels;
 		return m;
 	}