diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
index 10d3dc4..837614f 100644
--- a/drivers/mtd/mtdconcat.c
+++ b/drivers/mtd/mtdconcat.c
@@ -66,6 +66,8 @@
 	int ret = 0, err;
 	int i;
 
+	*retlen = 0;
+
 	for (i = 0; i < concat->num_subdev; i++) {
 		struct mtd_info *subdev = concat->subdev[i];
 		size_t size, retsize;
@@ -118,6 +120,8 @@
 	int err = -EINVAL;
 	int i;
 
+	*retlen = 0;
+
 	for (i = 0; i < concat->num_subdev; i++) {
 		struct mtd_info *subdev = concat->subdev[i];
 		size_t size, retsize;