diff --git a/include/seproxyhal_protocol.h b/include/seproxyhal_protocol.h
index efb52c6ff..9ab5ea8d4 100644
--- a/include/seproxyhal_protocol.h
+++ b/include/seproxyhal_protocol.h
@@ -59,6 +59,8 @@ static inline bool seph_parse_header(const uint8_t *buf, size_t size, seph_t *se
     return status;
 }
 
+#define SEPROXYHAL_TAG_INVALID (0x00)
+
 ////////////
 // EVENTS //
 ////////////