diff --git a/firmware/Pre-flight.md b/firmware/Pre-flight.md
index 183d1a6..702cd72 100644
--- a/firmware/Pre-flight.md
+++ b/firmware/Pre-flight.md
@@ -3,6 +3,7 @@
 - In `hw_config.h`
   - `USE_XOSC` is set. Otherwise the symbol timing frequency will be
     somewhat inaccurate.
+  - `RF_TX_ENABLE` is set
   - `APRS_ENABLE` is set if APRS is to be used on the flight
   - `APRS_USE_GEOFENCE` is set
   - `TELEMETRY_USE_GEOFENCE` is set