diff --git a/django/forms/utils.py b/django/forms/utils.py
index df75e94f81..16017ef418 100644
--- a/django/forms/utils.py
+++ b/django/forms/utils.py
@@ -5,7 +5,7 @@ import sys
 import warnings
 
 from django.conf import settings
-from django.utils.html import format_html, format_html_join
+from django.utils.html import format_html, format_html_join, escape
 from django.utils.encoding import force_text, python_2_unicode_compatible
 from django.utils import timezone
 from django.utils.translation import ugettext_lazy as _
@@ -55,8 +55,8 @@ class ErrorDict(dict):
     def as_data(self):
         return {f: e.as_data() for f, e in self.items()}
 
-    def as_json(self):
-        errors = {f: json.loads(e.as_json()) for f, e in self.items()}
+    def as_json(self, escape_html=False):
+        errors = {f: json.loads(e.as_json(escape_html=escape_html)) for f, e in self.items()}
         return json.dumps(errors)
 
     def as_ul(self):
@@ -86,11 +86,12 @@ class ErrorList(UserList, list):
     def as_data(self):
         return self.data
 
-    def as_json(self):
+    def as_json(self, escape_html=False):
         errors = []
         for error in ValidationError(self.data).error_list:
+            message = list(error)[0]
             errors.append({
-                'message': list(error)[0],
+                'message': escape(message) if escape_html else message,
                 'code': error.code or '',
             })
         return json.dumps(errors)
diff --git a/docs/ref/forms/api.txt b/docs/ref/forms/api.txt
index 5a9f6a1cdc..33fcf85511 100644
--- a/docs/ref/forms/api.txt
+++ b/docs/ref/forms/api.txt
@@ -142,7 +142,7 @@ and methods with an ``as_`` prefix could render them, but it had to be done
 the other way around in order not to break code that expects rendered error
 messages in ``Form.errors``.
 
-.. method:: Form.errors.as_json()
+.. method:: Form.errors.as_json(escape_html=False)
 
 .. versionadded:: 1.7
 
@@ -152,6 +152,17 @@ Returns the errors serialized as JSON.
     {"sender": [{"message": "Enter a valid email address.", "code": "invalid"}],
     "subject": [{"message": "This field is required.", "code": "required"}]}
 
+By default, ``as_json()`` does not escape its output. If you are using it for
+something like AJAX requests to a form view where the client interprets the
+response and inserts errors into the page, you'll want to be sure to escape the
+results on the client-side to avoid the possibility of a cross-site scripting
+attack. It's trivial to do so using a JavaScript library like jQuery - simply
+use ``$(el).text(errorText)`` rather than ``.html()``.
+
+If for some reason you don't want to use client-side escaping, you can also
+set ``escape_html=True`` and error messages will be escaped so you can use them
+directly in HTML.
+
 .. method:: Form.add_error(field, error)
 
 .. versionadded:: 1.7
diff --git a/tests/forms_tests/tests/test_forms.py b/tests/forms_tests/tests/test_forms.py
index f2a77cb089..f06a31f393 100644
--- a/tests/forms_tests/tests/test_forms.py
+++ b/tests/forms_tests/tests/test_forms.py
@@ -2071,6 +2071,33 @@ class FormsTestCase(TestCase):
         }
         self.assertEqual(errors, control)
 
+    def test_error_dict_as_json_escape_html(self):
+        """#21962 - adding html escape flag to ErrorDict"""
+        class MyForm(Form):
+            foo = CharField()
+            bar = CharField()
+
+            def clean(self):
+                raise ValidationError('<p>Non-field error.</p>',
+                                      code='secret',
+                                      params={'a': 1, 'b': 2})
+
+        control = {
+            'foo': [{'code': 'required', 'message': 'This field is required.'}],
+            'bar': [{'code': 'required', 'message': 'This field is required.'}],
+            '__all__': [{'code': 'secret', 'message': '<p>Non-field error.</p>'}]
+        }
+
+        form = MyForm({})
+        self.assertFalse(form.is_valid())
+
+        errors = json.loads(form.errors.as_json())
+        self.assertEqual(errors, control)
+
+        errors = json.loads(form.errors.as_json(escape_html=True))
+        control['__all__'][0]['message'] = '&lt;p&gt;Non-field error.&lt;/p&gt;'
+        self.assertEqual(errors, control)
+
     def test_error_list(self):
         e = ErrorList()
         e.append('Foo')