diff --git a/mt7921/main.c b/mt7921/main.c
index 269204494..7d91cf032 100644
--- a/mt7921/main.c
+++ b/mt7921/main.c
@@ -412,7 +412,8 @@ static int mt7921_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 	struct mt7921_sta *msta = sta ? (struct mt7921_sta *)sta->drv_priv :
 				  &mvif->sta;
 	struct mt76_wcid *wcid = &msta->wcid;
-	int idx = key->keyidx;
+	u8 *wcid_keyidx = &wcid->hw_key_idx;
+	int idx = key->keyidx, err = 0;
 
 	/* The hardware does not support per-STA RX GTK, fallback
 	 * to software mode for these.
@@ -428,6 +429,7 @@ static int mt7921_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 	switch (key->cipher) {
 	case WLAN_CIPHER_SUITE_AES_CMAC:
 		key->flags |= IEEE80211_KEY_FLAG_GENERATE_MMIE;
+		wcid_keyidx = &wcid->hw_key_idx2;
 		break;
 	case WLAN_CIPHER_SUITE_TKIP:
 	case WLAN_CIPHER_SUITE_CCMP:
@@ -442,16 +444,23 @@ static int mt7921_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 		return -EOPNOTSUPP;
 	}
 
-	if (cmd == SET_KEY) {
-		key->hw_key_idx = wcid->idx;
-		wcid->hw_key_idx = idx;
-	} else if (idx == wcid->hw_key_idx) {
-		wcid->hw_key_idx = -1;
-	}
+	mt7921_mutex_acquire(dev);
+
+	if (cmd == SET_KEY)
+		*wcid_keyidx = idx;
+	else if (idx == *wcid_keyidx)
+		*wcid_keyidx = -1;
+	else
+		goto out;
+
 	mt76_wcid_key_setup(&dev->mt76, wcid,
 			    cmd == SET_KEY ? key : NULL);
 
-	return mt7921_mcu_add_key(dev, vif, msta, key, cmd);
+	err = mt7921_mcu_add_key(dev, vif, msta, key, cmd);
+out:
+	mt7921_mutex_release(dev);
+
+	return err;
 }
 
 static int mt7921_config(struct ieee80211_hw *hw, u32 changed)