diff --git a/arch/um/drivers/cow_user.c b/arch/um/drivers/cow_user.c
index 0ec4052db9c5bbb183714a44012ef07fc388b026..6ab852bfcd3ac62cb66b18a02433d6b3feaadfcb 100644
--- a/arch/um/drivers/cow_user.c
+++ b/arch/um/drivers/cow_user.c
@@ -100,7 +100,7 @@ struct cow_header_v3_broken {
 	__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