diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index d0f9c4b0285c..b2700f8467ff 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -615,6 +615,9 @@ static int mtdchar_write_ioctl(struct mtd_info *mtd,
 	if (!usr_oob)
 		req.ooblen = 0;
 
+	req.len &= 0xffffffff;
+	req.ooblen &= 0xffffffff;
+
 	if (req.start + req.len > mtd->size)
 		return -EINVAL;
 
diff --git a/include/uapi/mtd/mtd-abi.h b/include/uapi/mtd/mtd-abi.h
index b869990c2db2..890d9e5b76d7 100644
--- a/include/uapi/mtd/mtd-abi.h
+++ b/include/uapi/mtd/mtd-abi.h
@@ -69,8 +69,8 @@ enum {
  * struct mtd_write_req - data structure for requesting a write operation
  *
  * @start:	start address
- * @len:	length of data buffer
- * @ooblen:	length of OOB buffer
+ * @len:	length of data buffer (only lower 32 bits are used)
+ * @ooblen:	length of OOB buffer (only lower 32 bits are used)
  * @usr_data:	user-provided data buffer
  * @usr_oob:	user-provided OOB buffer
  * @mode:	MTD mode (see "MTD operation modes")