diff --git a/tools/esp8266/config.h b/tools/esp8266/config.h
index 2efe5e4f..d33865c1 100644
--- a/tools/esp8266/config.h
+++ b/tools/esp8266/config.h
@@ -45,7 +45,7 @@
 #define DEF_RF24_CE_PIN         2
 #define DEF_RF24_IRQ_PIN        0
 
-// default radio ID
+/// default radio ID (the ending 01ULL NEEDS to remain unmodified!)
 #define DTU_RADIO_ID            ((uint64_t)0x1234567801ULL)
 
 // default NRF24 power, possible values (0 - 3)