diff --git a/sys/include/net/nanocoap.h b/sys/include/net/nanocoap.h
index c92b3f4e258fc..a0a2e04654446 100644
--- a/sys/include/net/nanocoap.h
+++ b/sys/include/net/nanocoap.h
@@ -2023,7 +2023,7 @@ static inline coap_method_flags_t coap_method2flag(unsigned code)
  * @returns     0 on success
  * @returns     <0 on error
  */
-int coap_parse(coap_pkt_t *pkt, uint8_t *buf, size_t len);
+int coap_parse(coap_pkt_t *pkt, const uint8_t *buf, size_t len);
 
 /**
  * @brief   Initialize a packet struct, to build a message buffer
diff --git a/sys/net/application_layer/gcoap/gcoap.c b/sys/net/application_layer/gcoap/gcoap.c
index 6c9a8a4e4a8ce..fe424ebed84dc 100644
--- a/sys/net/application_layer/gcoap/gcoap.c
+++ b/sys/net/application_layer/gcoap/gcoap.c
@@ -1633,12 +1633,34 @@ ssize_t gcoap_req_send_tl(const uint8_t *buf, size_t len,
      * response or request is confirmable) */
     if ((resp_handler != NULL) || (msg_type == COAP_TYPE_CON)) {
         mutex_lock(&_coap_state.lock);
-        /* Find empty slot in list of open requests. */
-        for (int i = 0; i < CONFIG_GCOAP_REQ_WAITING_MAX; i++) {
-            if (_coap_state.open_reqs[i].state == GCOAP_MEMO_UNUSED) {
-                memo = &_coap_state.open_reqs[i];
-                memo->state = GCOAP_MEMO_WAIT;
-                break;
+        coap_pkt_t req;
+        /* Uargh *cough*, ahem yes.. I know, I hate it too :'(
+         * TODO: either make this less depressing, via API refactoring.
+         * Or we just drop this for now and rely on implicit deregistration
+         * only (i.e., gcoap_obs_req_forget()). */
+        ssize_t res = coap_parse(&req, buf, len);
+        assert(res == 0);
+
+        if (coap_has_observe(&req)) {
+            uint32_t obsval = coap_get_observe(&req);
+            if (obsval == COAP_OBS_REGISTER ||
+                obsval == COAP_OBS_DEREGISTER) {
+                /* Reuse memo of the existing observe request.
+                 * This is needed because the new request to be sent semantically
+                 * belongs to the already existing request.
+                 * Otherwise, this would initiate another request with the same
+                 * token and one of them would never be removed. */
+                memo = _find_req_memo_by_pdu_token(&req, remote);
+            }
+        }
+        if (!memo) {
+            /* Find empty slot in list of open requests. */
+            for (int i = 0; i < CONFIG_GCOAP_REQ_WAITING_MAX; i++) {
+                if (_coap_state.open_reqs[i].state == GCOAP_MEMO_UNUSED) {
+                    memo = &_coap_state.open_reqs[i];
+                    memo->state = GCOAP_MEMO_WAIT;
+                    break;
+                }
             }
         }
         if (!memo) {
diff --git a/sys/net/application_layer/nanocoap/nanocoap.c b/sys/net/application_layer/nanocoap/nanocoap.c
index a058ae1232e53..af797204c3cd5 100644
--- a/sys/net/application_layer/nanocoap/nanocoap.c
+++ b/sys/net/application_layer/nanocoap/nanocoap.c
@@ -59,7 +59,7 @@ NANOCOAP_RESOURCE(well_known_core) COAP_WELL_KNOWN_CORE_DEFAULT_HANDLER;
 #define coap_resources_numof XFA_LEN(coap_resource_t, coap_resources_xfa)
 #endif
 
-static int _decode_value(unsigned val, uint8_t **pkt_pos_ptr, uint8_t *pkt_end);
+static int _decode_value(unsigned val, uint8_t **pkt_pos_ptr, const uint8_t *pkt_end);
 static uint32_t _decode_uint(uint8_t *pkt_pos, unsigned nbytes);
 static size_t _encode_uint(uint32_t *val);
 
@@ -76,13 +76,13 @@ static size_t _encode_uint(uint32_t *val);
  * |1 1 1 1 1 1 1 1|    Payload (if any) ...
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  */
-int coap_parse(coap_pkt_t *pkt, uint8_t *buf, size_t len)
+int coap_parse(coap_pkt_t *pkt, const uint8_t *buf, size_t len)
 {
     coap_hdr_t *hdr = (coap_hdr_t *)buf;
     pkt->hdr = hdr;
 
     uint8_t *pkt_pos = coap_hdr_data_ptr(hdr);
-    uint8_t *pkt_end = buf + len;
+    const uint8_t *pkt_end = buf + len;
 
     pkt->payload = NULL;
     pkt->payload_len = 0;
@@ -651,7 +651,7 @@ void coap_pkt_init(coap_pkt_t *pkt, uint8_t *buf, size_t len, size_t header_len)
  * return                -EBADMSG if val is 0xF, suggesting the full byte is
  *                                the 0xFF payload marker
  */
-static int _decode_value(unsigned val, uint8_t **pkt_pos_ptr, uint8_t *pkt_end)
+static int _decode_value(unsigned val, uint8_t **pkt_pos_ptr, const uint8_t *pkt_end)
 {
     uint8_t *pkt_pos = *pkt_pos_ptr;
     size_t left = pkt_end - pkt_pos;