diff --git a/tests/first_stage_test.py b/tests/first_stage_test.py
index ba12137d..d868f8b5 100644
--- a/tests/first_stage_test.py
+++ b/tests/first_stage_test.py
@@ -17,7 +17,7 @@ class CommandLineTest(testlib.RouterMixin, testlib.TestCase):
     #   * 3.x starting 2.7
 
     def test_valid_syntax(self):
-        stream = mitogen.parent.Stream(self.router, 0)
+        stream = mitogen.parent.Stream(self.router, 0, max_message_size=123)
         args = stream.get_boot_command()
 
         # Executing the boot command will print "EC0" and expect to read from