foo.diff

diff --git a/django/forms/utils.py b/django/forms/utils.py
index 3582384..4d44d28 100644
--- a/django/forms/utils.py
+++ b/django/forms/utils.py
@@ -127,6 +127,10 @@ class ErrorList(UserList):
             return list(error)[0]
         return force_text(error)
 
+    @classmethod
+    def __instancecheck__(cls, instance):
+        return isinstance(instance, (list, UserList))
+
 
 # Utilities for time zone support in DateTimeField et al.
 
diff --git a/tests/forms_tests/tests/test_forms.py b/tests/forms_tests/tests/test_forms.py
index 675565b..6197568 100644
--- a/tests/forms_tests/tests/test_forms.py
+++ b/tests/forms_tests/tests/test_forms.py
@@ -5,6 +5,7 @@ import copy
 import datetime
 import json
 import warnings
+from django.forms.util import ErrorList
 
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.core.validators import RegexValidator
@@ -2069,3 +2070,11 @@ class FormsTestCase(TestCase):
             '__all__': [{'code': 'secret', 'message': 'Non-field error.'}]
         }
         self.assertEqual(errors, control)
+
+    def test_error_list(self):
+        e = ErrorList()
+        self.assertTrue(isinstance(e, list))
+
+        e.append('Foo')
+        self.assertIn('Foo', e)
+        self.assertIn('Foo', forms.ValidationError(e))