diff --git a/kernel/sy_old/mars_light.c b/kernel/sy_old/mars_light.c
index 3fa31c1b..e7ccca08 100644
--- a/kernel/sy_old/mars_light.c
+++ b/kernel/sy_old/mars_light.c
@@ -443,8 +443,19 @@ int _set_if_params(struct mars_brick *_brick, void *private)
 		MARS_ERR("bad brick type\n");
 		return -EINVAL;
 	}
-	if (rot)
-		if_brick->dev_size = rot->dev_size;
+	if (!rot) {
+		MARS_ERR("too early\n");
+		return -EINVAL;
+	}
+	if (rot->dev_size <= 0) {
+		MARS_ERR("dev_size = %lld\n", rot->dev_size);
+		return -EINVAL;
+	}
+	if (if_brick->dev_size > 0 && rot->dev_size < if_brick->dev_size) {
+		MARS_ERR("new dev size = %lld < old dev_size = %lld\n", rot->dev_size, if_brick->dev_size);
+		return -EINVAL;
+	}
+	if_brick->dev_size = rot->dev_size;
 	if_brick->max_plugged = IF_MAX_PLUGGED;
 	if_brick->readahead = IF_READAHEAD;
 	if_brick->skip_sync = IF_SKIP_SYNC;