diff --git a/drivers/platform/chrome/cros_ec_proto_test.c b/drivers/platform/chrome/cros_ec_proto_test.c
index 5b9748e0463bcc..63e38671e95a64 100644
--- a/drivers/platform/chrome/cros_ec_proto_test.c
+++ b/drivers/platform/chrome/cros_ec_proto_test.c
@@ -2668,6 +2668,7 @@ static int cros_ec_proto_test_init(struct kunit *test)
 	ec_dev->dev->release = cros_ec_proto_test_release;
 	ec_dev->cmd_xfer = cros_kunit_ec_xfer_mock;
 	ec_dev->pkt_xfer = cros_kunit_ec_xfer_mock;
+	mutex_init(&ec_dev->lock);
 
 	priv->msg = (struct cros_ec_command *)priv->_msg;