diff --git a/sys/include/net/gcoap.h b/sys/include/net/gcoap.h
index e91748d11e02959a62f6d8d27eb884bbcdd8f7a8..bd475c74c0711887ccc43a8083e0dd9684c1e1b8 100644
--- a/sys/include/net/gcoap.h
+++ b/sys/include/net/gcoap.h
@@ -472,8 +472,9 @@ static inline ssize_t gcoap_request(coap_pkt_t *pdu, uint8_t *buf, size_t len,
  * @return length of the packet
  * @return 0 if cannot send
  */
-size_t gcoap_req_send2(uint8_t *buf, size_t len, sock_udp_ep_t *remote,
-                                                 gcoap_resp_handler_t resp_handler);
+size_t gcoap_req_send2(const uint8_t *buf, size_t len,
+                       const sock_udp_ep_t *remote,
+                       gcoap_resp_handler_t resp_handler);
 
 /**
  * @brief  Sends a buffer containing a CoAP request to the provided host/port.
@@ -489,8 +490,8 @@ size_t gcoap_req_send2(uint8_t *buf, size_t len, sock_udp_ep_t *remote,
  * @return length of the packet
  * @return 0 if cannot send
  */
-size_t gcoap_req_send(uint8_t *buf, size_t len, ipv6_addr_t *addr, uint16_t port,
-                                                gcoap_resp_handler_t resp_handler);
+size_t gcoap_req_send(const uint8_t *buf, size_t len, const ipv6_addr_t *addr,
+                      uint16_t port, gcoap_resp_handler_t resp_handler);
 
 /**
  * @brief  Initializes a CoAP response packet on a buffer.
@@ -557,7 +558,8 @@ int gcoap_obs_init(coap_pkt_t *pdu, uint8_t *buf, size_t len,
  * @return length of the packet
  * @return 0 if cannot send
  */
-size_t gcoap_obs_send(uint8_t *buf, size_t len, const coap_resource_t *resource);
+size_t gcoap_obs_send(const uint8_t *buf, size_t len,
+                      const coap_resource_t *resource);
 
 /**
  * @brief Provides important operational statistics.
diff --git a/sys/net/application_layer/coap/gcoap.c b/sys/net/application_layer/coap/gcoap.c
index 3e518bc5d4e1e214afb7058c360f2003ea627d6b..d441820f9d3a6ccdc3e3af3646b80c9d365b59fc 100644
--- a/sys/net/application_layer/coap/gcoap.c
+++ b/sys/net/application_layer/coap/gcoap.c
@@ -661,8 +661,8 @@ ssize_t gcoap_finish(coap_pkt_t *pdu, size_t payload_len, unsigned format)
     return _finish_pdu(pdu, (uint8_t *)pdu->hdr, len);
 }
 
-size_t gcoap_req_send(uint8_t *buf, size_t len, ipv6_addr_t *addr, uint16_t port,
-                                                 gcoap_resp_handler_t resp_handler)
+size_t gcoap_req_send(const uint8_t *buf, size_t len, const ipv6_addr_t *addr,
+                      uint16_t port, gcoap_resp_handler_t resp_handler)
 {
     sock_udp_ep_t remote;
 
@@ -675,8 +675,9 @@ size_t gcoap_req_send(uint8_t *buf, size_t len, ipv6_addr_t *addr, uint16_t port
     return gcoap_req_send2(buf, len, &remote, resp_handler);
 }
 
-size_t gcoap_req_send2(uint8_t *buf, size_t len, sock_udp_ep_t *remote,
-                                                 gcoap_resp_handler_t resp_handler)
+size_t gcoap_req_send2(const uint8_t *buf, size_t len,
+                       const sock_udp_ep_t *remote,
+                       gcoap_resp_handler_t resp_handler)
 {
     gcoap_request_memo_t *memo = NULL;
     assert(remote != NULL);
@@ -775,7 +776,8 @@ int gcoap_obs_init(coap_pkt_t *pdu, uint8_t *buf, size_t len,
     }
 }
 
-size_t gcoap_obs_send(uint8_t *buf, size_t len, const coap_resource_t *resource)
+size_t gcoap_obs_send(const uint8_t *buf, size_t len,
+                      const coap_resource_t *resource)
 {
     gcoap_observe_memo_t *memo = NULL;