diff --git a/drivers/mailbox/mailbox-test.c b/drivers/mailbox/mailbox-test.c
index 58d04726cdd7dc13f0faad15aeec89214ffce620..9ca96e9db6bfb137863250f8b27b2232fc1c449d 100644
--- a/drivers/mailbox/mailbox-test.c
+++ b/drivers/mailbox/mailbox-test.c
@@ -133,6 +133,7 @@ static ssize_t mbox_test_message_write(struct file *filp,
 out:
 	kfree(tdev->signal);
 	kfree(tdev->message);
+	tdev->signal = NULL;
 
 	return ret < 0 ? ret : count;
 }