diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index f2f482b..f79c0fa 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -1132,16 +1132,15 @@ static int mtdchar_mmap(struct file *file, struct vm_area_struct *vma)
 	struct mtd_file_info *mfi = file->private_data;
 	struct mtd_info *mtd = mfi->mtd;
 	struct map_info *map = mtd->priv;
-	unsigned long start;
-	unsigned long off;
-	u32 len;
+	resource_size_t start, off;
+	unsigned long len;
 
 	if (mtd->type == MTD_RAM || mtd->type == MTD_ROM) {
 		off = vma->vm_pgoff << PAGE_SHIFT;
 		start = map->phys;
 		len = PAGE_ALIGN((start & ~PAGE_MASK) + map->size);
 		start &= PAGE_MASK;
-		if ((vma->vm_end - vma->vm_start + off) > len)
+		if (off >= len || (vma->vm_end - vma->vm_start + off) > len)
 			return -EINVAL;
 
 		off += start;