diff --git a/changelog.d/13566.bugfix b/changelog.d/13566.bugfix
new file mode 100644
index 000000000..6c44024ad
--- /dev/null
+++ b/changelog.d/13566.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in Synapse 1.52.0 where sending server notices fails if `max_avatar_size` or `allowed_avatar_mimetypes` is set and not `system_mxid_avatar_url`.
\ No newline at end of file
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index d1909665d..65b9a655d 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -689,7 +689,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
                 errcode=Codes.BAD_JSON,
             )
 
-        if "avatar_url" in content:
+        if "avatar_url" in content and content.get("avatar_url") is not None:
             if not await self.profile_handler.check_avatar_size_and_mime_type(
                 content["avatar_url"],
             ):
diff --git a/tests/rest/admin/test_server_notice.py b/tests/rest/admin/test_server_notice.py
index 81e125e27..a2f347f66 100644
--- a/tests/rest/admin/test_server_notice.py
+++ b/tests/rest/admin/test_server_notice.py
@@ -159,6 +159,62 @@ class ServerNoticeTestCase(unittest.HomeserverTestCase):
         self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
         self.assertEqual("'msgtype' not in content", channel.json_body["error"])
 
+    @override_config(
+        {
+            "server_notices": {
+                "system_mxid_localpart": "notices",
+                "system_mxid_avatar_url": "somthingwrong",
+            },
+            "max_avatar_size": "10M",
+        }
+    )
+    def test_invalid_avatar_url(self) -> None:
+        """If avatar url in homeserver.yaml is invalid and
+        "check avatar size and mime type" is set, an error is returned.
+        TODO: Should be checked when reading the configuration."""
+        channel = self.make_request(
+            "POST",
+            self.url,
+            access_token=self.admin_user_tok,
+            content={
+                "user_id": self.other_user,
+                "content": {"msgtype": "m.text", "body": "test msg"},
+            },
+        )
+
+        self.assertEqual(500, channel.code, msg=channel.json_body)
+        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+
+    @override_config(
+        {
+            "server_notices": {
+                "system_mxid_localpart": "notices",
+                "system_mxid_display_name": "test display name",
+                "system_mxid_avatar_url": None,
+            },
+            "max_avatar_size": "10M",
+        }
+    )
+    def test_displayname_is_set_avatar_is_none(self) -> None:
+        """
+        Tests that sending a server notices is successfully,
+        if a display_name is set, avatar_url is `None` and
+        "check avatar size and mime type" is set.
+        """
+        channel = self.make_request(
+            "POST",
+            self.url,
+            access_token=self.admin_user_tok,
+            content={
+                "user_id": self.other_user,
+                "content": {"msgtype": "m.text", "body": "test msg"},
+            },
+        )
+        self.assertEqual(200, channel.code, msg=channel.json_body)
+
+        # user has one invite
+        self._check_invite_and_join_status(self.other_user, 1, 0)
+
     def test_server_notice_disabled(self) -> None:
         """Tests that server returns error if server notice is disabled"""
         channel = self.make_request(
diff --git a/tests/server_notices/test_resource_limits_server_notices.py b/tests/server_notices/test_resource_limits_server_notices.py
index e07ae78fc..bf403045e 100644
--- a/tests/server_notices/test_resource_limits_server_notices.py
+++ b/tests/server_notices/test_resource_limits_server_notices.py
@@ -11,16 +11,19 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
 from unittest.mock import Mock
 
+from twisted.test.proto_helpers import MemoryReactor
+
 from synapse.api.constants import EventTypes, LimitBlockingTypes, ServerNoticeMsgType
 from synapse.api.errors import ResourceLimitError
 from synapse.rest import admin
 from synapse.rest.client import login, room, sync
+from synapse.server import HomeServer
 from synapse.server_notices.resource_limits_server_notices import (
     ResourceLimitsServerNotices,
 )
+from synapse.util import Clock
 
 from tests import unittest
 from tests.test_utils import make_awaitable
@@ -52,7 +55,7 @@ class TestResourceLimitsServerNotices(unittest.HomeserverTestCase):
 
         return config
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.server_notices_sender = self.hs.get_server_notices_sender()
 
         # relying on [1] is far from ideal, but the only case where
@@ -251,7 +254,7 @@ class TestResourceLimitsServerNoticesWithRealRooms(unittest.HomeserverTestCase):
         c["admin_contact"] = "mailto:user@test.com"
         return c
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = self.hs.get_datastores().main
         self.server_notices_sender = self.hs.get_server_notices_sender()
         self.server_notices_manager = self.hs.get_server_notices_manager()