diff --git a/docs/releases/0.5.rst b/docs/releases/0.5.rst
index 6a848a684b..972b5252f5 100644
--- a/docs/releases/0.5.rst
+++ b/docs/releases/0.5.rst
@@ -96,7 +96,7 @@ If you created a Wagtail project prior to the release of Wagtail 0.3, it is like
 
 These entries (and the corresponding ``from wagtail.wagtail* import ...`` lines) need to be removed from ``urls.py``. (The entry for ``/admin/`` should be left in, however.)
 
-Since Wagtail 0.3, the wagtailadmin module automatically takes care of registering these URL subpaths, so these entries are redundant, and these urlconf modules are not guaranteed to remain stable and backwards-compatible in future. In particular, this release changes the definition of wagtail.wagtailimages.urls in a backwards-incompatible way - as a result, leaving the entry in place will cause image choosing to fail in some cases.
+Since Wagtail 0.3, the wagtailadmin module automatically takes care of registering these URL subpaths, so these entries are redundant, and these urlconf modules are not guaranteed to remain stable and backwards-compatible in future. Leaving these entries in place will now cause an ``ImproperlyConfigured`` exception to be thrown.
 
 
 New fields on Image and Rendition models
diff --git a/wagtail/wagtailimages/wagtail_hooks.py b/wagtail/wagtailimages/wagtail_hooks.py
index 3a039d9149..3347c42f0b 100644
--- a/wagtail/wagtailimages/wagtail_hooks.py
+++ b/wagtail/wagtailimages/wagtail_hooks.py
@@ -1,6 +1,7 @@
 from django.conf import settings
 from django.conf.urls import include, url
 from django.core import urlresolvers
+from django.core.exceptions import ImproperlyConfigured
 from django.utils.html import format_html, format_html_join
 from django.utils.translation import ugettext_lazy as _
 
@@ -17,8 +18,41 @@ def register_admin_urls():
     ]
 
 
+# Check for the presence of a pre-Wagtail-0.3-style urlconf, and fail loudly if one is found.
+# Prior to Wagtail 0.3, the standard Wagtail urls.py contained an entry for
+# wagtail.wagtailimages.urls rooted at '/admin/images/' or equivalent. As of Wagtail 0.5,
+# the wagtailimages admin views are defined by wagtail.wagtailimages.admin_urls, and
+# wagtail.wagtailimages.urls is used for front-end views instead - which means that those URLs
+# will clash with the admin.
+# This check can only be performed after the ROOT_URLCONF module has been fully imported. Since
+# importing a urlconf module generally involves recursively importing a whole load of other things
+# including models.py and wagtail_hooks.py, there is no obvious place to put this code at the
+# module level without causing a circular import. We therefore put it in construct_main_menu, which
+# is run frequently enough to ensure that the error message will not be missed. Yes, it's hacky :-(
+
+OLD_STYLE_URLCONF_CHECK_PASSED = False
+def check_old_style_urlconf():
+    global OLD_STYLE_URLCONF_CHECK_PASSED
+
+    # A faulty urls.py will place wagtail.wagtailimages.urls at the same path that
+    # wagtail.wagtailimages.admin_urls is loaded to, resulting in the wagtailimages_serve path
+    # being equal to wagtailimages_index followed by three arbitrary args
+    wagtailimages_serve_path = urlresolvers.reverse('wagtailimages_serve', args = ['123', '456', '789'])
+    wagtailimages_index_path = urlresolvers.reverse('wagtailimages_index')
+    if wagtailimages_serve_path == wagtailimages_index_path + '123/456/789/':
+        raise ImproperlyConfigured("""Your urls.py contains an entry for %s that needs to be removed.
+            See http://wagtail.readthedocs.org/en/latest/releases/0.5.html#urlconf-entries-for-admin-images-admin-embeds-etc-need-to-be-removed"""
+            % wagtailimages_index_path
+        )
+    else:
+        OLD_STYLE_URLCONF_CHECK_PASSED = True
+
+
 @hooks.register('construct_main_menu')
 def construct_main_menu(request, menu_items):
+    if not OLD_STYLE_URLCONF_CHECK_PASSED:
+        check_old_style_urlconf()
+
     if request.user.has_perm('wagtailimages.add_image'):
         menu_items.append(
             MenuItem(_('Images'), urlresolvers.reverse('wagtailimages_index'), classnames='icon icon-image', order=300)