diff --git a/sys/net/gnrc/application_layer/tftp/gnrc_tftp.c b/sys/net/gnrc/application_layer/tftp/gnrc_tftp.c
index 6cf78233dbfad72ef75a6df203c93408638049e4..0c952e73feaf816cd143779c0d84fccae33955f9 100644
--- a/sys/net/gnrc/application_layer/tftp/gnrc_tftp.c
+++ b/sys/net/gnrc/application_layer/tftp/gnrc_tftp.c
@@ -367,7 +367,7 @@ int _tftp_init_ctxt(ipv6_addr_t *addr, const char *file_name,
     /* generate a random source UDP source port */
     do {
         ctxt->src_port = (random_uint32() & 0xff) + GNRC_TFTP_DEFAULT_SRC_PORT;
-    } while (gnrc_netreg_num(GNRC_NETTYPE_UDP, ctxt->src_port));
+    } while (gnrc_netreg_lookup(GNRC_NETTYPE_UDP, ctxt->src_port));
 
     return TS_FINISHED;
 }
diff --git a/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c b/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c
index ee9619f4eabfbb277b00c8541422de2e04576597..fa6cf2097c68617bb8c3cc6da1b2903fd97d9d6c 100644
--- a/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c
+++ b/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c
@@ -219,7 +219,7 @@ static void _dispatch_next_header(gnrc_pktsnip_t *current, gnrc_pktsnip_t *pkt,
 
     /* dispatch IPv6 extension header only once */
     if (should_dispatch_current_type) {
-        bool should_release = (gnrc_netreg_num(GNRC_NETTYPE_IPV6, nh) == 0) &&
+        bool should_release = (!gnrc_netreg_lookup(GNRC_NETTYPE_IPV6, nh)) &&
                               (!interested);
 
         if (!should_release) {