diff --git a/changelog.d/13927.bugfix b/changelog.d/13927.bugfix
new file mode 100644
index 000000000..119cd128e
--- /dev/null
+++ b/changelog.d/13927.bugfix
@@ -0,0 +1 @@
+Fix a bug which prevented setting an avatar on homeservers which have an explicit port in their `server_name` and have `max_avatar_size` and/or `allowed_avatar_mimetypes` configuration. Contributed by @ashfame.
diff --git a/synapse/handlers/profile.py b/synapse/handlers/profile.py
index d8ff5289b..4bf9a047a 100644
--- a/synapse/handlers/profile.py
+++ b/synapse/handlers/profile.py
@@ -307,7 +307,11 @@ class ProfileHandler:
         if not self.max_avatar_size and not self.allowed_avatar_mimetypes:
             return True
 
-        server_name, _, media_id = parse_and_validate_mxc_uri(mxc)
+        host, port, media_id = parse_and_validate_mxc_uri(mxc)
+        if port is not None:
+            server_name = host + ":" + str(port)
+        else:
+            server_name = host
 
         if server_name == self.server_name:
             media_info = await self.store.get_local_media(media_id)
diff --git a/tests/handlers/test_profile.py b/tests/handlers/test_profile.py
index f88c725a4..675aa023a 100644
--- a/tests/handlers/test_profile.py
+++ b/tests/handlers/test_profile.py
@@ -14,6 +14,8 @@
 from typing import Any, Awaitable, Callable, Dict
 from unittest.mock import Mock
 
+from parameterized import parameterized
+
 from twisted.test.proto_helpers import MemoryReactor
 
 import synapse.types
@@ -327,6 +329,53 @@ class ProfileTestCase(unittest.HomeserverTestCase):
         )
         self.assertFalse(res)
 
+    @unittest.override_config(
+        {"server_name": "test:8888", "allowed_avatar_mimetypes": ["image/png"]}
+    )
+    def test_avatar_constraint_on_local_server_with_port(self):
+        """Test that avatar metadata is correctly fetched when the media is on a local
+        server and the server has an explicit port.
+
+        (This was previously a bug)
+        """
+        local_server_name = self.hs.config.server.server_name
+        media_id = "local"
+        local_mxc = f"mxc://{local_server_name}/{media_id}"
+
+        # mock up the existence of the avatar file
+        self._setup_local_files({media_id: {"mimetype": "image/png"}})
+
+        # and now check that check_avatar_size_and_mime_type is happy
+        self.assertTrue(
+            self.get_success(self.handler.check_avatar_size_and_mime_type(local_mxc))
+        )
+
+    @parameterized.expand([("remote",), ("remote:1234",)])
+    @unittest.override_config({"allowed_avatar_mimetypes": ["image/png"]})
+    def test_check_avatar_on_remote_server(self, remote_server_name: str) -> None:
+        """Test that avatar metadata is correctly fetched from a remote server"""
+        media_id = "remote"
+        remote_mxc = f"mxc://{remote_server_name}/{media_id}"
+
+        # if the media is remote, check_avatar_size_and_mime_type just checks the
+        # media cache, so we don't need to instantiate a real remote server. It is
+        # sufficient to poke an entry into the db.
+        self.get_success(
+            self.hs.get_datastores().main.store_cached_remote_media(
+                media_id=media_id,
+                media_type="image/png",
+                media_length=50,
+                origin=remote_server_name,
+                time_now_ms=self.clock.time_msec(),
+                upload_name=None,
+                filesystem_id="xyz",
+            )
+        )
+
+        self.assertTrue(
+            self.get_success(self.handler.check_avatar_size_and_mime_type(remote_mxc))
+        )
+
     def _setup_local_files(self, names_and_props: Dict[str, Dict[str, Any]]):
         """Stores metadata about files in the database.