diff --git a/src/nm-ip6-config.c b/src/nm-ip6-config.c
index e3fe92dbd3..89b8c1a665 100644
--- a/src/nm-ip6-config.c
+++ b/src/nm-ip6-config.c
@@ -183,7 +183,7 @@ const struct in6_addr *nm_ip6_config_get_ptp_address (NMIP6Config *config)
 	return &NM_IP6_CONFIG_GET_PRIVATE (config)->ptp_address;
 }
 
-void nm_ip6_config_set_ptp_address (NMIP6Config *config, struct in6_addr *ptp_addr)
+void nm_ip6_config_set_ptp_address (NMIP6Config *config, const struct in6_addr *ptp_addr)
 {
 	g_return_if_fail (NM_IS_IP6_CONFIG (config));
 
@@ -197,7 +197,7 @@ void nm_ip6_config_add_nameserver (NMIP6Config *config, const struct in6_addr *n
 	int i;
 
 	g_return_if_fail (NM_IS_IP6_CONFIG (config));
-	g_return_if_fail (nameserver > 0);
+	g_return_if_fail (nameserver != NULL);
 
 	priv = NM_IP6_CONFIG_GET_PRIVATE (config);
 
diff --git a/src/nm-ip6-config.h b/src/nm-ip6-config.h
index 4fd959d531..1e75a121c8 100644
--- a/src/nm-ip6-config.h
+++ b/src/nm-ip6-config.h
@@ -60,7 +60,7 @@ NMIP6Address *nm_ip6_config_get_address         (NMIP6Config *config, guint32 i)
 guint32       nm_ip6_config_get_num_addresses   (NMIP6Config *config);
 
 const struct in6_addr *nm_ip6_config_get_ptp_address (NMIP6Config *config);
-void          nm_ip6_config_set_ptp_address     (NMIP6Config *config, struct in6_addr *ptp_addr);
+void          nm_ip6_config_set_ptp_address     (NMIP6Config *config, const struct in6_addr *ptp_addr);
 
 void          nm_ip6_config_add_nameserver      (NMIP6Config *config, const struct in6_addr *nameserver);
 const struct in6_addr *nm_ip6_config_get_nameserver      (NMIP6Config *config, guint i);