diff --git a/sys/net/gnrc/network_layer/ndp/internal/gnrc_ndp_internal.c b/sys/net/gnrc/network_layer/ndp/internal/gnrc_ndp_internal.c
index fe6a892076..4a3158a2cd 100644
--- a/sys/net/gnrc/network_layer/ndp/internal/gnrc_ndp_internal.c
+++ b/sys/net/gnrc/network_layer/ndp/internal/gnrc_ndp_internal.c
@@ -346,8 +346,9 @@ void gnrc_ndp_internal_send_rtr_sol(kernel_pid_t iface, ipv6_addr_t *dst)
 static bool _pio_from_iface_addr(gnrc_pktsnip_t **res, gnrc_ipv6_netif_addr_t *addr,
                                  gnrc_pktsnip_t *next)
 {
-    if (((addr->prefix_len - 1U) < 127U) && /* 0 < prefix_len < 128 */
-        !ipv6_addr_is_unspecified(&addr->addr) &&
+    assert(((uint8_t) addr->prefix_len) <= 128U);
+
+    if (!ipv6_addr_is_unspecified(&addr->addr) &&
         !ipv6_addr_is_link_local(&addr->addr) &&
         !gnrc_ipv6_netif_addr_is_non_unicast(&addr->addr)) {
         DEBUG(" - PIO for %s/%" PRIu8 "\n", ipv6_addr_to_str(addr_str, &addr->addr,