diff --git a/example/tests/integration/test_polymorphism.py b/example/tests/integration/test_polymorphism.py
index 48ee80f3..bd33c3b3 100644
--- a/example/tests/integration/test_polymorphism.py
+++ b/example/tests/integration/test_polymorphism.py
@@ -145,7 +145,7 @@ def test_invalid_type_on_polymorphic_model(client):
     response = client.post(url, data=data)
     assert response.status_code == 409
     content = response.json()
-    assert len(content["errors"]) is 1
+    assert len(content["errors"]) == 1
     assert content["errors"][0]["status"] == "409"
     try:
         assert content["errors"][0]["detail"] == \
@@ -191,7 +191,7 @@ def test_invalid_type_on_polymorphic_relation(single_company, research_project_f
                           data=content)
     assert response.status_code == 409
     content = response.json()
-    assert len(content["errors"]) is 1
+    assert len(content["errors"]) == 1
     assert content["errors"][0]["status"] == "409"
     try:
         assert content["errors"][0]["detail"] == \
diff --git a/requirements-development.txt b/requirements-development.txt
index 55340b41..cf8ecb3b 100644
--- a/requirements-development.txt
+++ b/requirements-development.txt
@@ -4,7 +4,7 @@ django-filter==2.1.0
 django-polymorphic==2.0.3
 factory-boy==2.11.1
 Faker==1.0.2
-flake8==3.6.0
+flake8==3.7.5
 flake8-isort==2.6.0
 isort==4.3.4
 mock==2.0.0