diff --git a/ROMFS/px4fmu_common/init.d/rc.interface b/ROMFS/px4fmu_common/init.d/rc.interface
index c5d499a3e8b29c379a35d2d5b7f94b26f43ccee5..4f1a223ffc294efb08df9d0180d29c4c16eb2214 100644
--- a/ROMFS/px4fmu_common/init.d/rc.interface
+++ b/ROMFS/px4fmu_common/init.d/rc.interface
@@ -214,7 +214,7 @@ then
 		#
 		if [ $PWM_AUX_DISARMED != none -a $PWM_ACHDIS != none ]
 		then
-			pwm disarmed -c $PWM_ACHDIS -p $PWM_AUX_DISARMED -d $OUTPUT_AUX_DEV
+			pwm disarmed -c ${PWM_ACHDIS} -p ${PWM_AUX_DISARMED} -d ${OUTPUT_AUX_DEV}
 		fi
 
 		if [ $FAILSAFE_AUX != none ]