diff --git a/setup.py b/setup.py
index 52d12f7..f9f7c77 100644
--- a/setup.py
+++ b/setup.py
@@ -18,6 +18,7 @@ tests_require = [
     'pytest-cov==2.4.0',
     'pytest-django==3.1.2',
     'pytest-sugar==0.7.1',
+    'pytest-mock==1.6.3',
     'pytest==3.1.0',
     'wagtail_factories==0.3.0',
 ]
diff --git a/src/wagtail_personalisation/adapters.py b/src/wagtail_personalisation/adapters.py
index 5bde235..16260ec 100644
--- a/src/wagtail_personalisation/adapters.py
+++ b/src/wagtail_personalisation/adapters.py
@@ -175,7 +175,7 @@ class SessionSegmentsAdapter(BaseSegmentsAdapter):
         # Run tests on all remaining enabled segments to verify applicability.
         additional_segments = []
         for segment in enabled_segments:
-            if segment.is_static and self.request.session in segment.sessions.all():
+            if segment.is_static and self.request.session.session_key in segment.sessions.values_list('session_key', flat=True):
                 additional_segments.append(segment)
             elif not segment.is_static or not segment.is_full:
                 segment_rules = []
diff --git a/tests/unit/test_static_dynamic_segments.py b/tests/unit/test_static_dynamic_segments.py
index 53e30b1..7815d8e 100644
--- a/tests/unit/test_static_dynamic_segments.py
+++ b/tests/unit/test_static_dynamic_segments.py
@@ -73,3 +73,17 @@ def test_sessions_not_added_to_static_segment_if_rule_not_static():
         segment=segment)
 
     assert not segment.sessions.all()
+
+
+@pytest.mark.django_db
+def test_does_not_calculate_the_segment_again(rf, site, client, mocker):
+    session = client.session
+    session.save()
+    client.get(site.root_page.url)
+
+    segment = SegmentFactory(type=Segment.TYPE_STATIC, count=2)
+    VisitCountRule.objects.create(counted_page=site.root_page, segment=segment)
+
+    mock_test_rule = mocker.patch('wagtail_personalisation.adapters.SessionSegmentsAdapter._test_rules')
+    client.get(site.root_page.url)
+    assert mock_test_rule.call_count == 0