diff --git a/kittens/runner.py b/kittens/runner.py
index bb560dfc5..92f933ece 100644
--- a/kittens/runner.py
+++ b/kittens/runner.py
@@ -50,15 +50,26 @@ def launch(args):
     os.environ['KITTY_CONFIG_DIRECTORY'] = config_dir
     from kittens.tui.operations import clear_screen, reset_mode
     m = import_kitten_main_module(config_dir, kitten)
-    result = m['start'](args)
+    try:
+        result = m['start'](args)
+    finally:
+        sys.stdin = sys.__stdin__
     print(reset_mode('ALTERNATE_SCREEN') + clear_screen(), end='')
     if result is not None:
         import json
-        print('OK:', json.dumps(result))
+        data = json.dumps(result)
+        print('OK:', len(data), data)
     sys.stderr.flush()
     sys.stdout.flush()
 
 
+def deserialize(output):
+    import json
+    if output.startswith('OK: '):
+        prefix, sz, rest = output.split(' ', 2)
+        return json.loads(rest[:int(sz)])
+
+
 def run_kitten(kitten):
     import runpy
     kitten = resolved_kitten(kitten)
diff --git a/kitty/boss.py b/kitty/boss.py
index d60f92151..3c0bf2420 100644
--- a/kitty/boss.py
+++ b/kitty/boss.py
@@ -498,7 +498,7 @@ class Boss:
                 SpecialWindow(
                     ['kitty', '+runpy', 'from kittens.runner import main; main()'] + args,
                     stdin=data,
-                    env={'KITTY_COMMON_OPTS': json.dumps(copts)},
+                    env={'KITTY_COMMON_OPTS': json.dumps(copts), 'PYTHONWARNINGS': 'ignore'},
                     overlay_for=w.id))
             overlay_window.action_on_close = partial(self.on_kitten_finish, w.id, end_kitten)
 
@@ -510,8 +510,9 @@ class Boss:
 
     def on_kitten_finish(self, target_window_id, end_kitten, source_window):
         output = self.get_output(source_window, num_lines=None)
-        if output.startswith('OK: '):
-            data = json.loads(output.partition(' ')[2].strip())
+        from kittens.runner import deserialize
+        data = deserialize(output)
+        if data is not None:
             end_kitten(data, target_window_id, self)
 
     def input_unicode_character(self):