diff --git a/meta-isar/conf/multiconfig/qemuarm64-bookworm.conf b/meta-isar/conf/multiconfig/qemuarm64-bookworm.conf
index a04c9d1f..714e4d73 100644
--- a/meta-isar/conf/multiconfig/qemuarm64-bookworm.conf
+++ b/meta-isar/conf/multiconfig/qemuarm64-bookworm.conf
@@ -5,5 +5,5 @@
 MACHINE ?= "qemuarm64"
 DISTRO ?= "debian-bookworm"
 
-IMAGE_FSTYPES += "wic.xz"
+IMAGE_FSTYPES:append = " wic.xz"
 IMAGER_INSTALL += "${GRUB_BOOTLOADER_INSTALL}"