diff --git a/support/testing/tests/fs/test_ext.py b/support/testing/tests/fs/test_ext.py
index 0fe8af7e6d..2a6e0c4274 100644
--- a/support/testing/tests/fs/test_ext.py
+++ b/support/testing/tests/fs/test_ext.py
@@ -31,7 +31,7 @@ def boot_img_and_check_fs_type(emulator, builddir, fs_type):
                   kernel="builtin",
                   kernel_cmdline=["root=/dev/mmcblk0",
                                   "rootfstype={}".format(fs_type)],
-                  options=["-drive", "file={},if=sd".format(img)])
+                  options=["-drive", "file={},if=sd,format=raw".format(img)])
     emulator.login()
     _, exit_code = emulator.run(CHECK_FS_TYPE_CMD.format(fs_type))
     return exit_code