diff --git a/wagtail/tests/utils.py b/wagtail/tests/utils.py
index da5bfcb3a3..986afd54b3 100644
--- a/wagtail/tests/utils.py
+++ b/wagtail/tests/utils.py
@@ -136,11 +136,41 @@ class WagtailTestUtils(object):
                     return False
         return True
 
-    def _count_tag_occurrences(self, needle, haystack):
-        count = 1 if self._tag_is_equal(needle, haystack) else 0
+    def _tag_matches_with_extra_attrs(self, thin_tag, fat_tag):
+        # return true if thin_tag and fat_tag have the same name,
+        # and all attributes on thin_tag exist on fat_tag
+        if not hasattr(thin_tag, 'name') or not hasattr(fat_tag, 'name'):
+            return False
+        if thin_tag.name != fat_tag.name:
+            return False
+        for attr, value in thin_tag.attributes:
+            if value is None:
+                # attributes without a value is same as attribute with value that
+                # equals the attributes name:
+                # <input checked> == <input checked="checked">
+                if (attr, None) not in fat_tag.attributes and (attr, attr) not in fat_tag.attributes:
+                    return False
+            else:
+                if (attr, value) not in fat_tag.attributes:
+                    return False
+
+        return True
+
+    def _count_tag_occurrences(self, needle, haystack, allow_extra_attrs=False):
+        count = 0
+
+        if allow_extra_attrs:
+            if self._tag_matches_with_extra_attrs(needle, haystack):
+                count += 1
+        else:
+            if self._tag_is_equal(needle, haystack):
+                count += 1
 
         if hasattr(haystack, 'children'):
-            count += sum(self._count_tag_occurrences(needle, child) for child in haystack.children)
+            count += sum(
+                self._count_tag_occurrences(needle, child, allow_extra_attrs=allow_extra_attrs)
+                for child in haystack.children
+            )
 
         return count
 
@@ -160,10 +190,10 @@ class WagtailTestUtils(object):
                 for script_tag in self._find_template_script_tags(child):
                     yield script_tag
 
-    def assertTagInHTML(self, needle, haystack, count=None, msg_prefix=''):
+    def assertTagInHTML(self, needle, haystack, count=None, msg_prefix='', allow_extra_attrs=False):
         needle = assert_and_parse_html(self, needle, None, 'First argument is not valid HTML:')
         haystack = assert_and_parse_html(self, haystack, None, 'Second argument is not valid HTML:')
-        real_count = self._count_tag_occurrences(needle, haystack)
+        real_count = self._count_tag_occurrences(needle, haystack, allow_extra_attrs=allow_extra_attrs)
         if count is not None:
             self.assertEqual(
                 real_count, count,
diff --git a/wagtail/wagtailcore/tests/test_tests.py b/wagtail/wagtailcore/tests/test_tests.py
index 8756361de4..2f034f0b39 100644
--- a/wagtail/wagtailcore/tests/test_tests.py
+++ b/wagtail/wagtailcore/tests/test_tests.py
@@ -29,6 +29,20 @@ class TestAssertTagInHTML(TestCase, WagtailTestUtils):
         with self.assertRaises(AssertionError):
             self.assertTagInHTML('<li lang="en" class="important really" data-extra="boom">', haystack)
 
+    def test_assert_tag_in_html_with_extra_attrs(self):
+        haystack = """<ul>
+            <li class="normal">hugh</li>
+            <li class="normal">pugh</li>
+            <li class="really important" lang="en"><em>barney</em> mcgrew</li>
+        </ul>"""
+        self.assertTagInHTML('<li class="important really">', haystack, allow_extra_attrs=True)
+        self.assertTagInHTML('<li>', haystack, count=3, allow_extra_attrs=True)
+
+        with self.assertRaises(AssertionError):
+            self.assertTagInHTML('<li class="normal" lang="en">', haystack, allow_extra_attrs=True)
+        with self.assertRaises(AssertionError):
+            self.assertTagInHTML('<li class="important really">', haystack, count=2, allow_extra_attrs=True)
+
     def test_assert_tag_in_template_script(self):
         haystack = """<html>
             <script type="text/template">