diff --git a/sys/include/net/gnrc/pkt.h b/sys/include/net/gnrc/pkt.h
index 07eb593c4cbea0a143ef25847c0237b7fbbd7b6e..74f19fd93a59dc4840908098cc56f027c8f72cdd 100644
--- a/sys/include/net/gnrc/pkt.h
+++ b/sys/include/net/gnrc/pkt.h
@@ -129,7 +129,7 @@ typedef struct gnrc_pktsnip {
  *
  * @return  length of the list of headers.
  */
-static inline size_t gnrc_pkt_len(gnrc_pktsnip_t *pkt)
+static inline size_t gnrc_pkt_len(const gnrc_pktsnip_t *pkt)
 {
     size_t len = 0;
 
@@ -149,7 +149,7 @@ static inline size_t gnrc_pkt_len(gnrc_pktsnip_t *pkt)
  *
  * @return  length of the list of headers.
  */
-static inline size_t gnrc_pkt_len_upto(gnrc_pktsnip_t *pkt, gnrc_nettype_t type)
+static inline size_t gnrc_pkt_len_upto(const gnrc_pktsnip_t *pkt, gnrc_nettype_t type)
 {
     size_t len = 0;