diff --git a/sigtools/_signatures.py b/sigtools/_signatures.py
index db53000..dd1441e 100644
--- a/sigtools/_signatures.py
+++ b/sigtools/_signatures.py
@@ -89,7 +89,8 @@ def _is_co_flag_enabled(obj):
     if not feature:
         return False
 
-    if feature.mandatory and sys.version_info >= feature.mandatory:
+    mandatory_release = feature.getMandatoryRelease()
+    if mandatory_release and sys.version_info >= mandatory_release:
         return True
 
     try:
diff --git a/sigtools/tests/test_sphinxext.py b/sigtools/tests/test_sphinxext.py
index 6af170b..da18484 100644
--- a/sigtools/tests/test_sphinxext.py
+++ b/sigtools/tests/test_sphinxext.py
@@ -23,7 +23,7 @@
 
 import unittest
 
-from sigtools.tests import sphinxextfixt
+from sigtools.tests import sphinxextfixt, util
 
 
 app = object()
@@ -74,6 +74,7 @@ def test_inst_attr(self):
             None, {}, None, None)
         self.assertEqual((None, None), r)
 
+    @unittest.skipUnless(*util.python_has_optional_future_annotations)
     def test_attrs_class(self):
         r = self.sphinxext.process_signature(
             app, '', 'sigtools.tests.sphinxextfixt.AttrsClass',
diff --git a/sigtools/tests/util.py b/sigtools/tests/util.py
index d5cc40e..ba6990d 100644
--- a/sigtools/tests/util.py
+++ b/sigtools/tests/util.py
@@ -23,6 +23,7 @@
 import warnings
 from collections import defaultdict
 from functools import partial
+import __future__
 
 import unittest
 from repeated_test import tup, WithTestClass, with_options_matrix
@@ -175,12 +176,20 @@ def downgrade_param(self, param: funcsigs.Parameter):
 Fixtures = WithTestClass(SignatureTests)
 
 
-python_has_future_annotations = (3, 7, 0, "final") <= sys.version_info < (3, 11)
-python_has_annotations = (3, 11) <= sys.version_info
+python_has_future_annotations = hasattr(__future__, "annotations")
+python_has_annotations = (
+        python_has_future_annotations
+        and __future__.annotations.getMandatoryRelease()
+        and __future__.annotations.getMandatoryRelease() <= sys.version_info
+)
 python_doesnt_have_future_annotations = (
-    (sys.version_info < (3, 7, 0, "final")),
+    not python_has_future_annotations,
     "Python version does not have __future__.annotations"
 )
+python_has_optional_future_annotations = (
+    python_has_future_annotations and not python_has_annotations,
+    "Python version does not have optional __future__.annotations"
+)
 
 
 def signature_not_using_future_annotations(*args, **kwargs):