diff --git a/oscar/core/compat.py b/oscar/core/compat.py
index a84ba067f55..43103328c53 100644
--- a/oscar/core/compat.py
+++ b/oscar/core/compat.py
@@ -37,9 +37,6 @@ def get_user_model():
     raise ImproperlyConfigured("AUTH_USER_MODEL must be of the form"
                                " 'app_label.model_name'")
 
-_user_fields = get_user_model()._meta.fields
-VALID_USER_FORM_FIELD_NAMES = set([field.name for field in _user_fields])
-
 
 def existing_user_fields(fields):
     """
@@ -47,8 +44,17 @@ def existing_user_fields(fields):
     longer safe to assume the User model has certain fields. This helper
     function assists in writing portable forms Meta.fields definitions
     when those contain fields on the User model
+
+    Usage:
+    class UserForm(forms.Form):
+        ...
+        class Meta:
+            # won't break if first_name is not defined on User model
+            fields = existing_user_fields(['first_name', 'last_name'])
     """
-    return list(set(fields) & VALID_USER_FORM_FIELD_NAMES)
+    user_fields = get_user_model()._meta.fields
+    user_field_names = [field.name for field in user_fields]
+    return list(set(fields) & set(user_field_names))
 
 #
 # Python3 compatibility layer
diff --git a/tests/integration/customer/test_custom_user_model.py b/tests/integration/customer/test_custom_user_model.py
index 32d54bace73..ccd985110b8 100644
--- a/tests/integration/customer/test_custom_user_model.py
+++ b/tests/integration/customer/test_custom_user_model.py
@@ -1,12 +1,12 @@
 from django.test import TestCase
 from oscar.apps.customer.forms import ProfileForm
-from oscar.core import compat
+from oscar.core.compat import get_user_model, existing_user_fields
 
 
-class TestCustomUserModel(TestCase):
+class TestACustomUserModel(TestCase):
 
     def setUp(self):
-        self.user_klass = compat.get_user_model()
+        self.user_klass = get_user_model()
 
     def test_can_be_created_without_error(self):
         try:
@@ -14,8 +14,8 @@ def test_can_be_created_without_error(self):
         except Exception, e:
             self.fail("Unable to create user model: %s" % e)
 
-    def test_extra_field_is_picked_up(self):
-        self.assertTrue('extra_field' in compat.VALID_USER_FORM_FIELD_NAMES)
+    def test_extra_field_is_accessible(self):
+        self.assertTrue('extra_field' in existing_user_fields(['extra_field']))
         self.assertTrue(hasattr(self.user_klass(), 'extra_field'))
 
     def test_profile_form_doesnt_expose_extra_field(self):