diff --git a/conf/machine/sysmocom-idu.conf b/conf/machine/sysmocom-idu.conf
index 6140afc..83bd105 100644
--- a/conf/machine/sysmocom-idu.conf
+++ b/conf/machine/sysmocom-idu.conf
@@ -16,7 +16,7 @@ MACHINE_FEATURES += "kernel26 x86 usbhost pci acpi"
 
 KERNEL_IMAGETYPE = "bzImage"
 
-IMAGE_FSTYPES ?= "tar.gz ext4"
+IMAGE_FSTYPES = "tar.gz ext4"
 
 SERIAL_CONSOLE = "115200 ttyS0"
 MACHINE_CONSOLE = "console=ttyS0,115200n8"