diff --git a/ROMFS/px4fmu_common/init.d/rc.interface b/ROMFS/px4fmu_common/init.d/rc.interface
index 32af46b510..eceff0f99a 100644
--- a/ROMFS/px4fmu_common/init.d/rc.interface
+++ b/ROMFS/px4fmu_common/init.d/rc.interface
@@ -11,7 +11,7 @@ then
 	# Load main mixer
 	#
 
-	if [ $MIXER_AUX == none  -a $USE_IO == yes]
+	if [ $MIXER_AUX == none  -a $USE_IO == yes ]
 	then
 		set MIXER_AUX $MIXER.aux
 	fi