diff --git a/arch/um/drivers/cow_user.c b/arch/um/drivers/cow_user.c
index 61951b721268f1c030279cff98b2a25213708ca8..afdf1ea0f5576a1b1e860d922e05417341e3df45 100644
--- a/arch/um/drivers/cow_user.c
+++ b/arch/um/drivers/cow_user.c
@@ -75,7 +75,7 @@ struct cow_header_v3 {
 	__u32 alignment;
 	__u32 cow_format;
 	char backing_file[PATH_LEN_V3];
-};
+} __attribute__((packed));
 
 /* COW format definitions - for now, we have only the usual COW bitmap */
 #define COW_BITMAP 0