diff --git a/ROMFS/px4fmu_common/init.d/rc.fw_interface b/ROMFS/px4fmu_common/init.d/rc.fw_interface
index 1bf7a0e0300..133b65218a0 100644
--- a/ROMFS/px4fmu_common/init.d/rc.fw_interface
+++ b/ROMFS/px4fmu_common/init.d/rc.fw_interface
@@ -18,7 +18,7 @@ set MIXERSD /fs/microsd/etc/mixers/FMU_$FRAME_GEOMETRY.mix
 #Use the mixer file from the sd-card if it exists
 if [ -f $MIXERSD ]
 then
-	set MIXER MIXERSD
+	set MIXER $MIXERSD
 else
 	set MIXER /etc/mixers/FMU_$FRAME_GEOMETRY.mix
 fi