diff --git a/ahk/_async/engine.py b/ahk/_async/engine.py
index ab0c068..01cff8d 100644
--- a/ahk/_async/engine.py
+++ b/ahk/_async/engine.py
@@ -1101,6 +1101,8 @@ async def key_state(
             if mode not in ('T', 'P'):
                 raise ValueError(f'Invalid value for mode parameter. Mode must be `T` or `P`. Got {mode!r}')
             args.append(mode)
+        else:
+            args.append('')
         resp = await self._transport.function_call('AHKKeyState', args, blocking=blocking)
         return resp
 
diff --git a/ahk/_sync/engine.py b/ahk/_sync/engine.py
index 9e2df2d..bdfeb63 100644
--- a/ahk/_sync/engine.py
+++ b/ahk/_sync/engine.py
@@ -1089,6 +1089,8 @@ def key_state(
             if mode not in ('T', 'P'):
                 raise ValueError(f'Invalid value for mode parameter. Mode must be `T` or `P`. Got {mode!r}')
             args.append(mode)
+        else:
+            args.append('')
         resp = self._transport.function_call('AHKKeyState', args, blocking=blocking)
         return resp