diff --git a/build_library/vm_image_util.sh b/build_library/vm_image_util.sh
index 578fb32e30..b2f1500819 100644
--- a/build_library/vm_image_util.sh
+++ b/build_library/vm_image_util.sh
@@ -372,7 +372,7 @@ _write_base_cpio_disk() {
     mkdir -p "${root_mnt}"
 
     # Roll the rootfs into the CPIO
-    sudo mount -o loop "${TEMP_ROOTFS}" "${root_mnt}"
+    sudo mount -o loop,ro "${TEMP_ROOTFS}" "${root_mnt}"
     _write_dir_to_cpio "${root_mnt}" "$2"
     cp "${root_mnt}"/boot/vmlinuz "${dst_dir}/${vmlinuz_name}"
     sudo umount "${root_mnt}"