diff --git a/tests/test_local.py b/tests/test_local.py
index 2344f5f..3f41301 100644
--- a/tests/test_local.py
+++ b/tests/test_local.py
@@ -8,6 +8,9 @@ import trio
 import tractor
 
 
+from conftest import tractor_test
+
+
 @pytest.mark.trio
 async def test_no_arbitter():
     """An arbitter must be established before any nurseries
@@ -21,6 +24,13 @@ async def test_no_arbitter():
             pass
 
 
+def test_no_main():
+    """An async function **must** be passed to ``tractor.run()``.
+    """
+    with pytest.raises(TypeError):
+        tractor.run(None)
+
+
 def test_local_actor_async_func(arb_addr):
     """Verify a simple async function in-process.
     """
diff --git a/tractor/__init__.py b/tractor/__init__.py
index eccd5f7..d48e257 100644
--- a/tractor/__init__.py
+++ b/tractor/__init__.py
@@ -43,7 +43,7 @@ async def _main(
     """Async entry point for ``tractor``.
     """
     log = get_logger('tractor')
-    main = partial(async_fn, *args) if async_fn else None
+    main = partial(async_fn, *args)
     arbiter_addr = (host, port) = arbiter_addr or (
             _default_arbiter_host, _default_arbiter_port)
     get_console_log(kwargs.get('loglevel', get_loglevel()))