diff --git a/sys/include/net/nanocoap.h b/sys/include/net/nanocoap.h
index ab2b350240..5e3ffb4b9a 100644
--- a/sys/include/net/nanocoap.h
+++ b/sys/include/net/nanocoap.h
@@ -175,7 +175,7 @@ extern "C" {
 /**
  * @brief   Nanocoap-specific value to indicate no format specified
  */
-#define COAP_FORMAT_NONE        (65535)
+#define COAP_FORMAT_NONE        (UINT16_MAX)
 
 /**
  * @name    Nanocoap specific maximum values
diff --git a/sys/net/application_layer/gcoap/gcoap.c b/sys/net/application_layer/gcoap/gcoap.c
index ac0f770337..fe7236e6f4 100644
--- a/sys/net/application_layer/gcoap/gcoap.c
+++ b/sys/net/application_layer/gcoap/gcoap.c
@@ -38,6 +38,12 @@
 #define GCOAP_RESOURCE_WRONG_METHOD -1
 #define GCOAP_RESOURCE_NO_PATH -2
 
+/*
+ * gcoap internal Content-Format option value. Not intended for use in a
+ * transmitted packet. Must be a 3-byte unsigned value.
+ */
+#define COAP_FORMAT_NO_PAYLOAD  (UINT16_MAX + 1)
+
 /* Internal functions */
 static void *_event_loop(void *arg);
 static void _listen(sock_udp_t *sock);