diff --git a/tools/test-runner.c b/tools/test-runner.c
index 13a5de4..1fc95d3 100644
--- a/tools/test-runner.c
+++ b/tools/test-runner.c
@@ -214,7 +214,7 @@ static char *const qemu_argv[] = {
 	"-m", "256M",
 	"-net", "none",
 	"-no-reboot",
-	"-fsdev", "local,id=fsdev-root,path=/,readonly,security_model=none,"
+	"-fsdev", "local,id=fsdev-root,path=/,readonly=on,security_model=none,"
 	"multidevs=remap",
 	"-device", "virtio-9p-pci,fsdev=fsdev-root,mount_tag=/dev/root",
 	"-chardev", "stdio,id=con,mux=on",