diff --git a/sound/usb/6fire/control.c b/sound/usb/6fire/control.c
index 10104cb42165..020e9676d106 100644
--- a/sound/usb/6fire/control.c
+++ b/sound/usb/6fire/control.c
@@ -20,6 +20,7 @@
 #include "control.h"
 #include "comm.h"
 #include "chip.h"
+#include "pcm.h"
 
 static const char * const opt_coax_texts[2] = { "Optical", "Coax" };
 static const char * const line_phono_texts[2] = { "Line", "Phono" };
@@ -383,6 +384,12 @@ static int usb6fire_control_digital_thru_put(struct snd_kcontrol *kcontrol,
 	struct control_runtime *rt = snd_kcontrol_chip(kcontrol);
 	int changed = 0;
 
+	/*
+	 * with Digital Thru on, streaming_update() selects the altsetting and
+	 * writes the clock register of an idle card; prepare does the same
+	 * under stream_mutex
+	 */
+	guard(mutex)(&rt->chip->pcm->stream_mutex);
 	if (rt->digital_thru_switch != ucontrol->value.integer.value[0]) {
 		rt->digital_thru_switch = ucontrol->value.integer.value[0];
 		usb6fire_control_streaming_update(rt);