diff --git a/ROMFS/px4fmu_common/init.d/rc.mc_defaults b/ROMFS/px4fmu_common/init.d/rc.mc_defaults
index 6506ed8c3e5..34820781656 100644
--- a/ROMFS/px4fmu_common/init.d/rc.mc_defaults
+++ b/ROMFS/px4fmu_common/init.d/rc.mc_defaults
@@ -16,6 +16,7 @@ then
 	param set RTL_DESCEND_ALT 10.0
 fi
 
+# set environment variables (!= parameters)
 set PWM_RATE 400
 set PWM_DISARMED 900
 set PWM_MIN 1075