diff --git a/src/core/ipv6/nd6.c b/src/core/ipv6/nd6.c
index ffa135b9..d56d4e92 100644
--- a/src/core/ipv6/nd6.c
+++ b/src/core/ipv6/nd6.c
@@ -62,6 +62,9 @@
 
 #include <string.h>
 
+#if LWIP_IPV6_DUP_DETECT_ATTEMPTS > IP6_ADDR_TENTATIVE_COUNT_MASK
+#error LWIP_IPV6_DUP_DETECT_ATTEMPTS > IP6_ADDR_TENTATIVE_COUNT_MASK
+#endif
 
 /* Router tables. */
 struct nd6_neighbor_cache_entry neighbor_cache[LWIP_ND6_NUM_NEIGHBORS];
@@ -805,13 +808,13 @@ nd6_tmr(void)
   for (netif = netif_list; netif != NULL; netif = netif->next) {
     for (i = 0; i < LWIP_IPV6_NUM_ADDRESSES; ++i) {
       if (ip6_addr_istentative(netif->ip6_addr_state[i])) {
-        if ((netif->ip6_addr_state[i] & 0x07) >= LWIP_IPV6_DUP_DETECT_ATTEMPTS) {
+        if ((netif->ip6_addr_state[i] & IP6_ADDR_TENTATIVE_COUNT_MASK) >= LWIP_IPV6_DUP_DETECT_ATTEMPTS) {
           /* No NA received in response. Mark address as valid. */
           netif->ip6_addr_state[i] = IP6_ADDR_PREFERRED;
           /* @todo implement preferred and valid lifetimes. */
         } else if (netif->flags & NETIF_FLAG_UP) {
 #if LWIP_IPV6_MLD
-          if ((netif->ip6_addr_state[i] & 0x07) == 0) {
+          if ((netif->ip6_addr_state[i] & IP6_ADDR_TENTATIVE_COUNT_MASK) == 0) {
             /* Join solicited node multicast group. */
             ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(netif, i)->addr[3]);
             mld6_joingroup(netif_ip6_addr(netif, i), &multicast_address);
diff --git a/src/include/lwip/ip6_addr.h b/src/include/lwip/ip6_addr.h
index 665e75f2..622fee0a 100644
--- a/src/include/lwip/ip6_addr.h
+++ b/src/include/lwip/ip6_addr.h
@@ -263,6 +263,8 @@ Little-endian version, stored in network order (no htonl). */
 #define IP6_ADDR_PREFERRED    0x30
 #define IP6_ADDR_DEPRECATED   0x50
 
+#define IP6_ADDR_TENTATIVE_COUNT_MASK 0x07 /* 1-7 probes sent */
+
 #define ip6_addr_isinvalid(addr_state) (addr_state == IP6_ADDR_INVALID)
 #define ip6_addr_istentative(addr_state) (addr_state & IP6_ADDR_TENTATIVE)
 #define ip6_addr_isvalid(addr_state) (addr_state & IP6_ADDR_VALID) /* Include valid, preferred, and deprecated. */
diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 24a9fc68..0c499841 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -2214,7 +2214,7 @@
 #endif
 
 /**
- * LWIP_IPV6_DUP_DETECT_ATTEMPTS: Number of duplicate address detection attempts.
+ * LWIP_IPV6_DUP_DETECT_ATTEMPTS=[0..7]: Number of duplicate address detection attempts.
  */
 #if !defined LWIP_IPV6_DUP_DETECT_ATTEMPTS || defined __DOXYGEN__
 #define LWIP_IPV6_DUP_DETECT_ATTEMPTS   1