diff --git a/src/include/netif/etharp.h b/src/include/netif/etharp.h
index f9da367d..634f4db2 100644
--- a/src/include/netif/etharp.h
+++ b/src/include/netif/etharp.h
@@ -118,7 +118,7 @@ PACK_STRUCT_END
 #define ETHTYPE_ARP 0x0806
 #define ETHTYPE_IP  0x0800
 
-/** ARP message types */
+/** ARP message types (opcodes) */
 #define ARP_REQUEST 1
 #define ARP_REPLY   2
 
@@ -144,7 +144,10 @@ err_t etharp_query(struct netif *netif, struct ip_addr *ipaddr, struct pbuf *q);
 err_t etharp_request(struct netif *netif, struct ip_addr *ipaddr);
 
 #if LWIP_AUTOIP
-err_t etharp_raw(struct netif *netif, struct eth_addr *ethsrc_addr, struct eth_addr *ethdst_addr, struct eth_addr *hwsrc_addr, struct ip_addr *ipsrc_addr,  struct eth_addr *hwdst_addr, struct ip_addr *ipdst_addr, unsigned short int OpCode);
+err_t etharp_raw(struct netif *netif, struct eth_addr *ethsrc_addr, struct eth_addr *ethdst_addr,
+                 struct eth_addr *hwsrc_addr, struct ip_addr *ipsrc_addr,
+                 struct eth_addr *hwdst_addr, struct ip_addr *ipdst_addr,
+                 unsigned short int opcode);
 #endif /* LWIP_AUTOIP */
 
 #define eth_addr_cmp(addr1, addr2) (memcmp((addr1)->addr, (addr2)->addr, 6) == 0)