diff --git a/nox/_parametrize.py b/nox/_parametrize.py
index 8b5d55c3..ad83b53a 100644
--- a/nox/_parametrize.py
+++ b/nox/_parametrize.py
@@ -78,7 +78,7 @@ def __eq__(self, other: object) -> bool:
         elif isinstance(other, dict):
             return dict(zip(self.arg_names, self.args)) == other
 
-        raise NotImplementedError
+        return NotImplemented
 
 
 def _apply_param_specs(param_specs: Iterable[Param], f: Any) -> Any:
diff --git a/tests/test__parametrize.py b/tests/test__parametrize.py
index 1364087d..41ea4236 100644
--- a/tests/test__parametrize.py
+++ b/tests/test__parametrize.py
@@ -35,8 +35,7 @@ def test_param_eq(param, other, expected):
 
 
 def test_param_eq_fail():
-    with pytest.raises(NotImplementedError):
-        _parametrize.Param() == "a"  # noqa: B015
+    assert _parametrize.Param() != "a"
 
 
 def test_parametrize_decorator_one():