diff --git a/sys/net/ethernet.h b/sys/net/ethernet.h
index 8d512c06e66e..1b89416b9b64 100644
--- a/sys/net/ethernet.h
+++ b/sys/net/ethernet.h
@@ -68,7 +68,12 @@ struct	ether_header {
  */
 struct	ether_addr {
 	u_char octet[ETHER_ADDR_LEN];
-};
+} __packed;
+
+#ifdef CTASSERT
+CTASSERT(sizeof (struct ether_header) == ETHER_ADDR_LEN * 2 + 2);
+CTASSERT(sizeof (struct ether_addr) == ETHER_ADDR_LEN);
+#endif
 
 #define	ETHER_IS_MULTICAST(addr) (*(addr) & 0x01) /* is address mcast/bcast? */