diff --git a/sys/include/net/ethertype.h b/sys/include/net/ethertype.h
index 5fb7b727b4..b35fb0152b 100644
--- a/sys/include/net/ethertype.h
+++ b/sys/include/net/ethertype.h
@@ -38,6 +38,23 @@ extern "C" {
 #define ETHERTYPE_NDN           (0x8624)    /**< NDN Protocol (http://named-data.net/) */
 #define ETHERTYPE_IPV6          (0x86dd)    /**< Internet protocol version 6 */
 #define ETHERTYPE_6LOENC        (0xa0ed)    /**< 6LoWPAN encapsulation */
+
+/**
+ * @defgroup    net_ethertype_custom_config Custom ethertype
+ * @ingroup     config
+ * @brief       Custom ethertype definition
+ * @warning     Do not use a IANA assigned number
+ * @see         https://www.iana.org/assignments/ieee-802-numbers/ieee-802-numbers.xhtml
+ *
+ * @{
+ */
+#ifndef ETHERTYPE_CUSTOM
+#define ETHERTYPE_CUSTOM        (0x0101)    /**< Custom ethertype */
+#endif
+/**
+ * @}
+ */
+
 #define ETHERTYPE_UNKNOWN       (0xffff)    /**< Reserved (no protocol specified) */
 
 #ifdef __cplusplus
diff --git a/sys/include/net/gnrc/nettype.h b/sys/include/net/gnrc/nettype.h
index af2f7d729f..0297634c99 100644
--- a/sys/include/net/gnrc/nettype.h
+++ b/sys/include/net/gnrc/nettype.h
@@ -90,6 +90,17 @@ typedef enum {
      * @}
      */
 
+    /**
+     * @{
+     * @name Link layer
+     */
+#if IS_USED(MODULE_GNRC_NETTYPE_CUSTOM) || defined(DOXYGEN)
+    GNRC_NETTYPE_CUSTOM,            /**< Custom ethertype */
+#endif
+    /**
+     * @}
+     */
+
     /**
      * @{
      * @name Network layer
@@ -177,6 +188,10 @@ static inline gnrc_nettype_t gnrc_nettype_from_ethertype(uint16_t type)
 #if IS_USED(MODULE_GNRC_SIXLOENC) && IS_USED(MODULE_GNRC_NETTYPE_SIXLOWPAN)
         case ETHERTYPE_6LOENC:
             return GNRC_NETTYPE_SIXLOWPAN;
+#endif
+#if IS_USED(MODULE_GNRC_NETTYPE_CUSTOM)
+        case ETHERTYPE_CUSTOM:
+            return GNRC_NETTYPE_CUSTOM;
 #endif
         default:
             return GNRC_NETTYPE_UNDEF;
@@ -211,6 +226,10 @@ static inline uint16_t gnrc_nettype_to_ethertype(gnrc_nettype_t type)
 #if IS_USED(MODULE_GNRC_NETTYPE_NDN)
         case GNRC_NETTYPE_NDN:
             return ETHERTYPE_NDN;
+#endif
+#if IS_USED(MODULE_GNRC_NETTYPE_CUSTOM)
+        case GNRC_NETTYPE_CUSTOM:
+            return ETHERTYPE_CUSTOM;
 #endif
         default:
             return ETHERTYPE_UNKNOWN;