diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 927cb34c4805..7c426d07a555 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -274,7 +274,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 			if (bitmap->offset < 0) {
 				/* DATA  BITMAP METADATA  */
 				if (bitmap->offset
-				    + page->index * (PAGE_SIZE/512)
+				    + (long)(page->index * (PAGE_SIZE/512))
 				    + size/512 > 0)
 					/* bitmap runs in to metadata */
 					return -EINVAL;