diff --git a/examples/protocols/coap_server/main/coap_server_example_main.c b/examples/protocols/coap_server/main/coap_server_example_main.c
index b3ea703080..0d2ce0a284 100644
--- a/examples/protocols/coap_server/main/coap_server_example_main.c
+++ b/examples/protocols/coap_server/main/coap_server_example_main.c
@@ -51,8 +51,7 @@ send_async_response(coap_context_t *ctx, const coap_endpoint_t *local_if)
     coap_pdu_t *response;
     unsigned char buf[3];
     const char* response_data     = "Hello World!";
-    size_t size = sizeof(coap_hdr_t) + 20;
-    response = coap_pdu_init(async->flags & COAP_MESSAGE_CON, COAP_RESPONSE_CODE(205), 0, size);
+    response = coap_pdu_init(async->flags & COAP_MESSAGE_CON, COAP_RESPONSE_CODE(205), 0, COAP_MAX_PDU_SIZE);
     response->hdr->id = coap_new_message_id(ctx);
     if (async->tokenlen)
         coap_add_token(response, async->tokenlen, async->token);