diff --git a/single_ursim_control/main.py b/single_ursim_control/main.py
index ceb017c..0a8351d 100644
--- a/single_ursim_control/main.py
+++ b/single_ursim_control/main.py
@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 import sys
+from typing import Optional
 from config import Config
 from plugins import SleepPlugin, SyncPlugin, WaitPlugin, URRTDEPlugin, LogPlugin
 from plugin_repository import PluginRepository
@@ -15,7 +16,7 @@ from program_loader import load_program
 
 class HTTPControl:
 
-    def __init__(self, executor: ProgramExecutor, wait_plugin: WaitPlugin):
+    def __init__(self, executor: ProgramExecutor, wait_plugin: Optional[WaitPlugin]):
         self._executor_ref = weakref.ref(executor)
 
         if wait_plugin: