diff --git a/src/core/ipv4/dhcp.c b/src/core/ipv4/dhcp.c
index abff34d..eaae34d 100644
--- a/src/core/ipv4/dhcp.c
+++ b/src/core/ipv4/dhcp.c
@@ -108,21 +108,23 @@
  * This might be moved into the struct dhcp (not necessarily since
  * lwIP is single-threaded and the array is only used while in recv
  * callback). */
-#define DHCP_OPTION_IDX_OVERLOAD    0
-#define DHCP_OPTION_IDX_MSG_TYPE    1
-#define DHCP_OPTION_IDX_SERVER_ID   2
-#define DHCP_OPTION_IDX_LEASE_TIME  3
-#define DHCP_OPTION_IDX_T1          4
-#define DHCP_OPTION_IDX_T2          5
-#define DHCP_OPTION_IDX_SUBNET_MASK 6
-#define DHCP_OPTION_IDX_ROUTER      7
-#define DHCP_OPTION_IDX_DNS_SERVER  8
+enum dhcp_option_idx {
+  DHCP_OPTION_IDX_OVERLOAD = 0,
+  DHCP_OPTION_IDX_MSG_TYPE,
+  DHCP_OPTION_IDX_SERVER_ID,
+  DHCP_OPTION_IDX_LEASE_TIME,
+  DHCP_OPTION_IDX_T1,
+  DHCP_OPTION_IDX_T2,
+  DHCP_OPTION_IDX_SUBNET_MASK,
+  DHCP_OPTION_IDX_ROUTER,
+  DHCP_OPTION_IDX_DNS_SERVER,
+  DHCP_OPTION_IDX_DNS_SERVER_LAST = DHCP_OPTION_IDX_DNS_SERVER + DNS_MAX_SERVERS - 1,
 #if LWIP_DHCP_GET_NTP_SRV
-#define DHCP_OPTION_IDX_NTP_SERVER  (DHCP_OPTION_IDX_DNS_SERVER + DNS_MAX_SERVERS)
-#define DHCP_OPTION_IDX_MAX         (DHCP_OPTION_IDX_NTP_SERVER + LWIP_DHCP_MAX_NTP_SERVERS)
-#else /* LWIP_DHCP_GET_NTP_SRV */
-#define DHCP_OPTION_IDX_MAX         (DHCP_OPTION_IDX_DNS_SERVER + DNS_MAX_SERVERS)
+  DHCP_OPTION_IDX_NTP_SERVER,
+  DHCP_OPTION_IDX_NTP_SERVER_LAST = DHCP_OPTION_IDX_NTP_SERVER + LWIP_DHCP_MAX_NTP_SERVERS - 1,
 #endif /* LWIP_DHCP_GET_NTP_SRV */
+  DHCP_OPTION_IDX_MAX
+};
 
 /** Holds the decoded option values, only valid while in dhcp_recv.
     @todo: move this into struct dhcp? */