diff --git a/grub2_theme_preview/__main__.py b/grub2_theme_preview/__main__.py
index 58170c1..d5b32d5 100644
--- a/grub2_theme_preview/__main__.py
+++ b/grub2_theme_preview/__main__.py
@@ -546,7 +546,7 @@ def _inner_main(options):
                     run_command.append('-full-screen')
                 if is_efi_host:
                     run_command += [
-                        '-drive', f'if=pflash,format=raw,readonly,file={omvf_image_path}'
+                        '-drive', f'if=pflash,format=raw,readonly=on,file={omvf_image_path}'
                     ]
 
                 print('INFO: Please give GRUB a moment to show up in QEMU...')