diff --git a/sys/include/net/gcoap.h b/sys/include/net/gcoap.h
index 47c25c65fd..1cc757d8a0 100644
--- a/sys/include/net/gcoap.h
+++ b/sys/include/net/gcoap.h
@@ -184,7 +184,8 @@
  * gcoap includes server and client capability. Available features include:
  *
  * - Message Type: Supports non-confirmable (NON) messaging. Additionally
- *   provides a callback on timeout.
+ *   provides a callback on timeout. Provides piggybacked ACK response to a
+ *   confirmable (CON) request.
  * - Observe extension: Provides server-side registration and notifications.
  * - Server and Client provide helper functions for writing the
  *   response/request. See the CoAP topic in the source documentation for
diff --git a/sys/net/application_layer/coap/gcoap.c b/sys/net/application_layer/coap/gcoap.c
index 0bfb0c376b..0483431014 100644
--- a/sys/net/application_layer/coap/gcoap.c
+++ b/sys/net/application_layer/coap/gcoap.c
@@ -137,9 +137,16 @@ static void _listen(sock_udp_t *sock)
 
     /* incoming request */
     if (coap_get_code_class(&pdu) == COAP_CLASS_REQ) {
-        size_t pdu_len = _handle_req(&pdu, buf, sizeof(buf), &remote);
-        if (pdu_len > 0) {
-            sock_udp_send(sock, buf, pdu_len, &remote);
+        if (coap_get_type(&pdu) == COAP_TYPE_NON
+                || coap_get_type(&pdu) == COAP_TYPE_CON) {
+            size_t pdu_len = _handle_req(&pdu, buf, sizeof(buf), &remote);
+            if (pdu_len > 0) {
+                sock_udp_send(sock, buf, pdu_len, &remote);
+            }
+        }
+        else {
+            DEBUG("gcoap: illegal request type: %u\n", coap_get_type(&pdu));
+            return;
         }
     }
     /* incoming response */
@@ -730,9 +737,10 @@ size_t gcoap_req_send2(const uint8_t *buf, size_t len,
 
 int gcoap_resp_init(coap_pkt_t *pdu, uint8_t *buf, size_t len, unsigned code)
 {
-    /* Assume NON type request, so response type is the same. */
+    if (coap_get_type(pdu) == COAP_TYPE_CON) {
+        coap_hdr_set_type(pdu->hdr, COAP_TYPE_ACK);
+    }
     coap_hdr_set_code(pdu->hdr, code);
-    /* Create message ID since NON? */
 
     /* Reserve some space between the header and payload to write options later */
     pdu->payload      = buf + coap_get_total_hdr_len(pdu) + GCOAP_RESP_OPTIONS_BUF;