diff --git a/drivers/video/sm501fb.c b/drivers/video/sm501fb.c
index 98f24f0..16d4f4c 100644
--- a/drivers/video/sm501fb.c
+++ b/drivers/video/sm501fb.c
@@ -1624,6 +1624,8 @@
 	if (!fbi)
 		return 0;
 
+	mutex_init(&info->fb[head]->mm_lock);
+
 	ret = sm501fb_init_fb(info->fb[head], head, drvname);
 	if (ret) {
 		dev_err(info->dev, "cannot initialise fb %s\n", drvname);