diff --git a/sys/net/application_layer/gcoap/gcoap.c b/sys/net/application_layer/gcoap/gcoap.c
index d52ccdf596..04954fcfb7 100644
--- a/sys/net/application_layer/gcoap/gcoap.c
+++ b/sys/net/application_layer/gcoap/gcoap.c
@@ -1630,6 +1630,14 @@ ssize_t gcoap_req_send_tl(const uint8_t *buf, size_t len,
     return ((res > 0 || res == -ENOTCONN) ? res : 0);
 }
 
+static void _add_generated_observe_option(coap_pkt_t *pdu)
+{
+        /* generate initial notification value */
+        uint32_t now       = ztimer_now(ZTIMER_MSEC);
+        pdu->observe_value = (now >> GCOAP_OBS_TICK_EXPONENT) & 0xFFFFFF;
+        coap_opt_add_uint(pdu, COAP_OPT_OBSERVE, pdu->observe_value);
+}
+
 int gcoap_resp_init(coap_pkt_t *pdu, uint8_t *buf, size_t len, unsigned code)
 {
     int header_len = coap_build_reply(pdu, code, buf, len, 0);
@@ -1644,10 +1652,7 @@ int gcoap_resp_init(coap_pkt_t *pdu, uint8_t *buf, size_t len, unsigned code)
     pdu->payload_len = len - header_len;
 
     if (coap_get_observe(pdu) == COAP_OBS_REGISTER) {
-        /* generate initial notification value */
-        uint32_t now       = ztimer_now(ZTIMER_MSEC);
-        pdu->observe_value = (now >> GCOAP_OBS_TICK_EXPONENT) & 0xFFFFFF;
-        coap_opt_add_uint(pdu, COAP_OPT_OBSERVE, pdu->observe_value);
+        _add_generated_observe_option(pdu);
     }
 
     return 0;
@@ -1672,9 +1677,7 @@ int gcoap_obs_init(coap_pkt_t *pdu, uint8_t *buf, size_t len,
     if (hdrlen > 0) {
         coap_pkt_init(pdu, buf, len, hdrlen);
 
-        uint32_t now       = ztimer_now(ZTIMER_MSEC);
-        pdu->observe_value = (now >> GCOAP_OBS_TICK_EXPONENT) & 0xFFFFFF;
-        coap_opt_add_uint(pdu, COAP_OPT_OBSERVE, pdu->observe_value);
+        _add_generated_observe_option(pdu);
 
         return GCOAP_OBS_INIT_OK;
     }