diff --git a/wagtail/tests/utils.py b/wagtail/tests/utils.py
index e5a9cbbdf..fd155e6b4 100644
--- a/wagtail/tests/utils.py
+++ b/wagtail/tests/utils.py
@@ -1,6 +1,5 @@
 from contextlib import contextmanager
 import warnings
-import threading
 
 from django.contrib.auth import get_user_model
 from django.utils import six
@@ -29,34 +28,3 @@ class WagtailTestUtils(object):
         for w in warning_list:
             if not issubclass(w.category, DeprecationWarning):
                 warnings.showwarning(message=w.message, category=w.category, filename=w.filename, lineno=w.lineno, file=w.file, line=w.line)
-
-
-# from http://www.caktusgroup.com/blog/2009/05/26/testing-django-views-for-concurrency-issues/
-def test_concurrently(times):
-    """
-    Add this decorator to small pieces of code that you want to test
-    concurrently to make sure they don't raise exceptions when run at the
-    same time.  E.g., some Django views that do a SELECT and then a subsequent
-    INSERT might fail when the INSERT assumes that the data has not changed
-    since the SELECT.
-    """
-    def test_concurrently_decorator(test_func):
-        def wrapper(*args, **kwargs):
-            exceptions = []
-            def call_test_func():
-                try:
-                    test_func(*args, **kwargs)
-                except Exception as e:
-                    exceptions.append(e)
-                    raise
-            threads = []
-            for i in range(times):
-                threads.append(threading.Thread(target=call_test_func))
-            for t in threads:
-                t.start()
-            for t in threads:
-                t.join()
-            if exceptions:
-                raise Exception('test_concurrently intercepted %s exceptions: %s' % (len(exceptions), exceptions))
-        return wrapper
-    return test_concurrently_decorator
diff --git a/wagtail/wagtailimages/tests/test_models.py b/wagtail/wagtailimages/tests/test_models.py
index 52f7d352c..fa3434417 100644
--- a/wagtail/wagtailimages/tests/test_models.py
+++ b/wagtail/wagtailimages/tests/test_models.py
@@ -11,7 +11,7 @@ from django.core.files.uploadedfile import SimpleUploadedFile
 from django.db.utils import IntegrityError
 from django.db import connection
 
-from wagtail.tests.utils import WagtailTestUtils, test_concurrently
+from wagtail.tests.utils import WagtailTestUtils
 from wagtail.wagtailcore.models import Page
 from wagtail.tests.models import EventPage, EventPageCarouselItem
 from wagtail.wagtailimages.models import Rendition, Filter, SourceImageIOError
@@ -372,27 +372,3 @@ class TestIssue312(TestCase):
             height=rend1.height,
             focal_point_key=rend1.focal_point_key,
         )
-
-    def test_duplicate_filters(self):
-        @test_concurrently(10)
-        def get_renditions():
-            # Create an image
-            image = Image.objects.create(
-                title="Concurrency test image",
-                file=get_test_image_file(),
-            )
-            # get renditions concurrently, using various filters that are unlikely to exist already
-            for width in range(10, 100, 10):
-                image.get_rendition('width-%d' % width)
-
-            image.delete()
-
-            # this block opens multiple database connections, which need to be closed explicitly
-            # so that we can drop the test database at the end of the test run
-            connection.close()
-
-        get_renditions()
-        # if the above has completed with no race conditions, there should be precisely one
-        # of each of the above filters in the database
-        for width in range(10, 100, 10):
-            self.assertEqual(Filter.objects.filter(spec='width-%d' % width).count(), 1)