diff --git a/monkeytype/cli.py b/monkeytype/cli.py
index 21a3a2f..ab85726 100644
--- a/monkeytype/cli.py
+++ b/monkeytype/cli.py
@@ -6,6 +6,7 @@
 import argparse
 import importlib
 import inspect
+import os
 import os.path
 import runpy
 import subprocess
@@ -41,6 +42,11 @@ def module_path(path: str) -> Tuple[str, Optional[str]]:
     parts = path.split(':', 1)
     module = parts.pop(0)
     qualname = parts[0] if parts else None
+    if os.sep in module:  # Smells like a path
+        raise argparse.ArgumentTypeError(
+            f'{module} does not look like a valid Python import path'
+        )
+
     return module, qualname
 
 
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 9816338..873af71 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -96,3 +96,12 @@ def test_cli_context_manager_activated(capsys, stdout, stderr):
     assert out == "IN SETUP: stub\nIN TEARDOWN: stub\n"
     assert err == ""
     assert ret == 0
+
+
+def test_pathlike_parameter(store_data, capsys):
+    store, db_file = store_data
+    with mock.patch.dict(os.environ, {DefaultConfig.DB_PATH_VAR: db_file.name}):
+        with pytest.raises(SystemExit):
+            cli.main(['stub', 'test/foo.py:bar'], stdout, stderr)
+        out, err = capsys.readouterr()
+        assert "test/foo.py does not look like a valid Python import path" in err