diff --git a/ROMFS/px4fmu_common/init.d-posix/rcS b/ROMFS/px4fmu_common/init.d-posix/rcS
index 059ff50fb672b789bf159d0106206cbb187ddecf..d8c0858ad01f70dd2bec91fe2dfb8a5de58ccae2 100644
--- a/ROMFS/px4fmu_common/init.d-posix/rcS
+++ b/ROMFS/px4fmu_common/init.d-posix/rcS
@@ -162,15 +162,15 @@ fi
 
 # Adapt timeout parameters if simulation runs faster or slower than realtime.
 if [ ! -z $PX4_SIM_SPEED_FACTOR ]; then
-	COM_DL_LOSS_T_LONGER=$(($PX4_SIM_SPEED_FACTOR * 10))
+	COM_DL_LOSS_T_LONGER=$((PX4_SIM_SPEED_FACTOR * 10))
 	echo "COM_DL_LOSS_T set to $COM_DL_LOSS_T_LONGER"
 	param set COM_DL_LOSS_T $COM_DL_LOSS_T_LONGER
 
-	COM_RC_LOSS_T_LONGER=$(($PX4_SIM_SPEED_FACTOR * 1))
+	COM_RC_LOSS_T_LONGER=$((PX4_SIM_SPEED_FACTOR * 1))
 	echo "COM_RC_LOSS_T set to $COM_RC_LOSS_T_LONGER"
 	param set COM_RC_LOSS_T $COM_RC_LOSS_T_LONGER
 
-	COM_OF_LOSS_T_LONGER=$(($PX4_SIM_SPEED_FACTOR * 10))
+	COM_OF_LOSS_T_LONGER=$((PX4_SIM_SPEED_FACTOR * 10))
 	echo "COM_OF_LOSS_T set to $COM_OF_LOSS_T_LONGER"
 	param set COM_OF_LOSS_T $COM_OF_LOSS_T_LONGER
 fi