diff --git a/sys/net/application_layer/gcoap/gcoap.c b/sys/net/application_layer/gcoap/gcoap.c
index e6fc5d91ff..6d016f6519 100644
--- a/sys/net/application_layer/gcoap/gcoap.c
+++ b/sys/net/application_layer/gcoap/gcoap.c
@@ -1664,13 +1664,19 @@ ssize_t gcoap_req_send(const uint8_t *buf, size_t len,
 
         switch (msg_type) {
         case COAP_TYPE_CON:
+            /* Can't store it for retransmission, even though sending it from
+             * the provided buffer once is possible */
+            if (len > CONFIG_GCOAP_PDU_BUF_SIZE) {
+                return -EINVAL;
+            }
+
             /* copy buf to resend_bufs record */
             memo->msg.data.pdu_buf = NULL;
             for (int i = 0; i < CONFIG_GCOAP_RESEND_BUFS_MAX; i++) {
                 if (!_coap_state.resend_bufs[i][0]) {
                     memo->msg.data.pdu_buf = &_coap_state.resend_bufs[i][0];
                     memcpy(memo->msg.data.pdu_buf, buf,
-                           CONFIG_GCOAP_PDU_BUF_SIZE);
+                           len);
                     memo->msg.data.pdu_len = len;
                     break;
                 }