diff --git a/include/netinet/arp.h b/include/netinet/arp.h
index b60a0a4f8d8e9..1f434ea1fa259 100644
--- a/include/netinet/arp.h
+++ b/include/netinet/arp.h
@@ -65,7 +65,7 @@
 
 /* All ARP ioctls take a pointer to a struct arpreq as their parameter: */
 
-struct arpreq
+struct aligned_data(sizeof(FAR void *)) arpreq
 {
   struct sockaddr arp_pa;                /* Protocol address */
   struct sockaddr arp_ha;                /* Hardware address */