diff --git a/block/vdi.c b/block/vdi.c
index dcbc27c9cbd40dec6f082849a1a0e9b80066937e..b6ec0020dcbf314674e576fba084ad948b47273a 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -165,7 +165,7 @@ typedef struct {
     uuid_t uuid_link;
     uuid_t uuid_parent;
     uint64_t unused2[7];
-} VdiHeader;
+} QEMU_PACKED VdiHeader;
 
 typedef struct {
     /* The block map entries are little endian (even in memory). */