diff --git a/djblets/avatars/registry.py b/djblets/avatars/registry.py
index 1a28e250f7bbb650ee2eff837ed174c7e128b93f..0896482d09ab110a7144e02afc666d9f1d254df2 100644
--- a/djblets/avatars/registry.py
+++ b/djblets/avatars/registry.py
@@ -123,11 +123,15 @@ class AvatarServiceRegistry(Registry):
             services = set(services)
 
         for service in services:
-            if not self.has_service(service.id):
+            if not self.has_service(service.avatar_service_id):
                 raise self.lookup_error_class(self.format_error(
-                    UNKNOWN_SERVICE_ENABLED, service_id=service.id))
+                    UNKNOWN_SERVICE_ENABLED,
+                    service_id=service.avatar_service_id))
 
-        self._enabled_services = {service.id for service in services}
+        self._enabled_services = {
+            service.avatar_service_id
+            for service in services
+        }
         default_service = self.default_service
 
         if (default_service is not None and
@@ -173,12 +177,13 @@ class AvatarServiceRegistry(Registry):
             self._default_service_id = None
         elif service not in self:
             raise self.lookup_error_class(self.format_error(
-                UNKNOWN_SERVICE_DEFAULT, service_id=service.id))
-        elif not self.is_enabled(service.id):
+                UNKNOWN_SERVICE_DEFAULT, service_id=service.avatar_service_id))
+        elif not self.is_enabled(service.avatar_service_id):
             raise DisabledServiceError(self.format_error(
-                DISABLED_SERVICE_DEFAULT, service_id=service.id))
+                DISABLED_SERVICE_DEFAULT,
+                service_id=service.avatar_service_id))
         else:
-            self._default_service_id = service.id
+            self._default_service_id = service.avatar_service_id
 
         if save:
             self.save()
@@ -225,7 +230,8 @@ class AvatarServiceRegistry(Registry):
         self._enabled_services.discard(service_id)
         default_service = self.default_service
 
-        if default_service is not None and default_service.id == service_id:
+        if (default_service is not None and
+            default_service.avatar_service_id == service_id):
             self.set_default_service(None)
 
         if save:
@@ -281,7 +287,7 @@ class AvatarServiceRegistry(Registry):
             djblets.avatars.errors.AvatarServiceNotFoundError:
                 Raised if the specified service cannot be found.
         """
-        self.disable_service(service.id)
+        self.disable_service(service.avatar_service_id)
         super(AvatarServiceRegistry, self).unregister(service)
 
     def populate(self):
diff --git a/djblets/avatars/services/base.py b/djblets/avatars/services/base.py
index 77c3cf42babb2a4f16c2a795f606adc65440ee15..d83876837b09e4b75e31cd7bc08eacfe70b37561 100644
--- a/djblets/avatars/services/base.py
+++ b/djblets/avatars/services/base.py
@@ -37,7 +37,7 @@ class AvatarService(object):
             user (django.contrib.auth.models.User):
                 The user for whom the avatar URLs are to be retrieved.
 
-            size (int, optional):
+            size (int):
                 The requested avatar size (height and width) in pixels.
 
         Returns:
diff --git a/djblets/avatars/tests.py b/djblets/avatars/tests.py
index 72b240dbfdecdc562c34d2af2def88100355062b..c974292caf46c1e14b440651d9ce3e8341e926f9 100644
--- a/djblets/avatars/tests.py
+++ b/djblets/avatars/tests.py
@@ -23,7 +23,7 @@ from djblets.testing.testcases import TestCase
 class DummyAvatarService(AvatarService):
     """An Avatar service for testing."""
 
-    id = 'dummy'
+    avatar_service_id = 'dummy'
     name = 'Dummy Avatar Service'
 
     def __init__(self, use_2x=False):
@@ -91,7 +91,7 @@ class AvatarServiceTests(SpyAgency, TestCase):
             service.render(HttpRequest(), self.user, 24),
             '<img src="http://example.com/avatar.png" alt="User Name"'
             ' width="24" height="24"'
-            ' srcset="http://example.com/avatar.png 1x">\n')
+            ' srcset="http://example.com/avatar.png 1x" class="avatar">\n')
 
     def test_render_2x(self):
         """Testing AvatarService.render at 2x resolution."""
@@ -101,7 +101,7 @@ class AvatarServiceTests(SpyAgency, TestCase):
             '<img src="http://example.com/avatar.png" alt="User Name"'
             ' width="24" height="24"'
             ' srcset="http://example.com/avatar.png 1x,'
-            ' http://example.com/avatar@2x.png 2x">\n')
+            ' http://example.com/avatar@2x.png 2x" class="avatar">\n')
 
     def test_get_avatar_urls_caching(self):
         """Testing AvatarService.get_avatar_urls caching"""
@@ -171,11 +171,11 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         service = DummyAvatarService()
 
         registry.register(service)
-        self.assertFalse(registry.is_enabled(service.id))
+        self.assertFalse(registry.is_enabled(service.avatar_service_id))
         self.assertSetEqual(set(registry.enabled_services), set())
 
-        registry.enable_service(service.id)
-        self.assertTrue(registry.is_enabled(service.id))
+        registry.enable_service(service.avatar_service_id)
+        self.assertTrue(registry.is_enabled(service.avatar_service_id))
         self.assertSetEqual(
             registry.enabled_services,
             {service})
@@ -183,15 +183,17 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
     def test_disable_service(self):
         """Testing AvatarServiceRegistry.disable_service"""
         registry = AvatarServiceRegistry()
-        self.assertFalse(registry.is_enabled(GravatarService.id))
-        registry.enable_service(GravatarService.id)
+        self.assertFalse(registry.is_enabled(
+            GravatarService.avatar_service_id))
+        registry.enable_service(GravatarService.avatar_service_id)
 
-        self.assertTrue(registry.is_enabled(GravatarService.id))
+        self.assertTrue(registry.is_enabled(GravatarService.avatar_service_id))
         self.assertSetEqual(set(registry.enabled_services),
                             set(registry))
 
-        registry.disable_service(GravatarService.id)
-        self.assertFalse(registry.is_enabled(GravatarService.id))
+        registry.disable_service(GravatarService.avatar_service_id)
+        self.assertFalse(registry.is_enabled(
+            GravatarService.avatar_service_id))
         self.assertSetEqual(set(registry.enabled_services), set())
 
     def test_set_enabled_services(self):
@@ -201,7 +203,8 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         dummy_service = DummyAvatarService()
         registry.register(dummy_service)
 
-        gravatar_service = registry.get('id', GravatarService.id)
+        gravatar_service = registry.get('avatar_service_id',
+                                        GravatarService.avatar_service_id)
 
         registry.enabled_services = [dummy_service, gravatar_service]
 
@@ -216,7 +219,8 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
 
         dummy_service = DummyAvatarService()
 
-        gravatar_service = registry.get('id', GravatarService.id)
+        gravatar_service = registry.get('avatar_service_id',
+                                        GravatarService.avatar_service_id)
 
         with self.assertRaises(ItemLookupError):
             registry.enabled_services = [dummy_service, gravatar_service]
@@ -228,7 +232,8 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         registry = AvatarServiceRegistry()
 
         dummy_serivce = DummyAvatarService()
-        gravatar_service = registry.get('id', GravatarService.id)
+        gravatar_service = registry.get('avatar_service_id',
+                                        GravatarService.avatar_service_id)
         registry.register(dummy_serivce)
         registry.enabled_services = [dummy_serivce, gravatar_service]
 
@@ -262,7 +267,8 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         disabled service
         """
         registry = AvatarServiceRegistry()
-        gravatar_service = registry.get('id', GravatarService.id)
+        gravatar_service = registry.get('avatar_service_id',
+                                        GravatarService.avatar_service_id)
 
         self.assertIsNone(registry.default_service)
 
@@ -278,15 +284,16 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         self.spy_on(logging.error)
 
         self.siteconfig.set(AvatarServiceRegistry.ENABLED_SERVICES_KEY,
-                            [GravatarService.id])
+                            [GravatarService.avatar_service_id])
         self.siteconfig.set(AvatarServiceRegistry.DEFAULT_SERVICE_KEY,
-                            GravatarService.id)
+                            GravatarService.avatar_service_id)
         self.siteconfig.save()
 
         registry = AvatarServiceRegistry()
         registry.populate()
 
-        gravatar_service = registry.get('id', GravatarService.id)
+        gravatar_service = registry.get('avatar_service_id',
+                                        GravatarService.avatar_service_id)
 
         self.assertTrue(registry.populated)
         self.assertEqual(registry.default_service, gravatar_service)
@@ -301,7 +308,7 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         self.spy_on(logging.error)
 
         self.siteconfig.set(AvatarServiceRegistry.DEFAULT_SERVICE_KEY,
-                            DummyAvatarService.id)
+                            DummyAvatarService.avatar_service_id)
         self.siteconfig.save()
 
         registry = AvatarServiceRegistry()
@@ -322,7 +329,7 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         self.spy_on(logging.error)
 
         self.siteconfig.set(AvatarServiceRegistry.DEFAULT_SERVICE_KEY,
-                            GravatarService.id)
+                            GravatarService.avatar_service_id)
         self.siteconfig.save()
 
         registry = AvatarServiceRegistry()
@@ -342,7 +349,7 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         """
         self.spy_on(logging.error)
         self.siteconfig.set(AvatarServiceRegistry.ENABLED_SERVICES_KEY,
-                            [DummyAvatarService.id])
+                            [DummyAvatarService.avatar_service_id])
         self.siteconfig.save()
 
         registry = AvatarServiceRegistry()
@@ -370,9 +377,9 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
 
         self.spy_on(logging.error)
         self.siteconfig.set(AvatarServiceRegistry.ENABLED_SERVICES_KEY,
-                            [DummyAvatarService.id])
+                            [DummyAvatarService.avatar_service_id])
         self.siteconfig.set(AvatarServiceRegistry.DEFAULT_SERVICE_KEY,
-                            DummyAvatarService.id)
+                            DummyAvatarService.avatar_service_id)
         self.siteconfig.save()
 
         registry = TestRegistry()
@@ -382,9 +389,10 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
     def test_unregister(self):
         """Testing AvatarServiceRegistry.unregister"""
         registry = AvatarServiceRegistry()
-        gravatar_service = registry.get('id', GravatarService.id)
+        gravatar_service = registry.get('avatar_service_id',
+                                        GravatarService.avatar_service_id)
 
-        registry.enable_service(GravatarService.id)
+        registry.enable_service(GravatarService.avatar_service_id)
 
         self.assertSetEqual(registry.enabled_services, {gravatar_service})
         registry.unregister(gravatar_service)
@@ -395,10 +403,12 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         service
         """
         registry = AvatarServiceRegistry()
-        registry.enable_service(GravatarService.id)
-        registry.set_default_service(registry.get('id', GravatarService.id))
+        registry.enable_service(GravatarService.avatar_service_id)
+        registry.set_default_service(
+            registry.get('avatar_service_id',
+                         GravatarService.avatar_service_id))
 
-        registry.disable_service(GravatarService.id)
+        registry.disable_service(GravatarService.avatar_service_id)
         self.assertIsNone(registry.default_service)
 
     def test_disable_default_from_setter(self):
@@ -406,8 +416,10 @@ class AvatarServiceRegistryTests(SpyAgency, TestCase):
         default services
         """
         registry = AvatarServiceRegistry()
-        registry.enable_service(GravatarService.id)
-        registry.set_default_service(registry.get('id', GravatarService.id))
+        registry.enable_service(GravatarService.avatar_service_id)
+        registry.set_default_service(
+            registry.get('avatar_service_id',
+                         GravatarService.avatar_service_id))
 
         registry.enabled_services = []
         self.assertIsNone(registry.default_service)
