diff --git a/tests/qemu-iotests/040 b/tests/qemu-iotests/040
index c284d08796..90b5b4f2ad 100755
--- a/tests/qemu-iotests/040
+++ b/tests/qemu-iotests/040
@@ -289,7 +289,7 @@ class TestSetSpeed(ImageCommitTestCase):
         qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % mid_img, test_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0x1 0 512', test_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xef 524288 524288', mid_img)
-        self.vm = iotests.VM().add_drive(test_img)
+        self.vm = iotests.VM().add_drive('blkdebug::' + test_img)
         self.vm.launch()
 
     def tearDown(self):