diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index 3b899e552a..665e3f76b8 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -1321,7 +1321,7 @@ class ModelAdmin(BaseModelAdmin):
         opts = model._meta
         app_label = opts.app_label
         action_list = LogEntry.objects.filter(
-            object_id = object_id,
+            object_id = unquote(object_id),
             content_type__id__exact = ContentType.objects.get_for_model(model).id
         ).select_related().order_by('action_time')
         # If no history was found, see whether this object even exists.
diff --git a/tests/regressiontests/admin_views/tests.py b/tests/regressiontests/admin_views/tests.py
index f074d77b11..937b086d40 100644
--- a/tests/regressiontests/admin_views/tests.py
+++ b/tests/regressiontests/admin_views/tests.py
@@ -1344,15 +1344,20 @@ class AdminViewStringPrimaryKeyTest(TestCase):
     def setUp(self):
         self.client.login(username='super', password='secret')
         content_type_pk = ContentType.objects.get_for_model(ModelWithStringPrimaryKey).pk
-        LogEntry.objects.log_action(100, content_type_pk, self.pk, self.pk, 2, change_message='')
+        LogEntry.objects.log_action(100, content_type_pk, self.pk, self.pk, 2, change_message='Changed something')
 
     def tearDown(self):
         self.client.logout()
 
     def test_get_history_view(self):
-        "Retrieving the history for the object using urlencoded form of primary key should work"
+        """
+        Retrieving the history for an object using urlencoded form of primary
+        key should work.
+        Refs #12349, #18550.
+        """
         response = self.client.get('/test_admin/admin/admin_views/modelwithstringprimarykey/%s/history/' % quote(self.pk))
         self.assertContains(response, escape(self.pk))
+        self.assertContains(response, 'Changed something')
         self.assertEqual(response.status_code, 200)
 
     def test_get_change_view(self):