diff --git a/changelog.d/6794.feature b/changelog.d/6794.feature
new file mode 100644
index 000000000..df9e4b77a
--- /dev/null
+++ b/changelog.d/6794.feature
@@ -0,0 +1 @@
+Implement updated authorization rules for aliases events, from [MSC2260](https://github.com/matrix-org/matrix-doc/pull/2260).
diff --git a/synapse/rest/client/v1/room.py b/synapse/rest/client/v1/room.py
index 5aef8238b..6f31584c5 100644
--- a/synapse/rest/client/v1/room.py
+++ b/synapse/rest/client/v1/room.py
@@ -184,6 +184,12 @@ class RoomStateEventRestServlet(TransactionRestServlet):
 
         content = parse_json_object_from_request(request)
 
+        if event_type == EventTypes.Aliases:
+            # MSC2260
+            raise SynapseError(
+                400, "Cannot send m.room.aliases events via /rooms/{room_id}/state"
+            )
+
         event_dict = {
             "type": event_type,
             "content": content,
@@ -231,6 +237,12 @@ class RoomSendEventRestServlet(TransactionRestServlet):
         requester = await self.auth.get_user_by_req(request, allow_guest=True)
         content = parse_json_object_from_request(request)
 
+        if event_type == EventTypes.Aliases:
+            # MSC2260
+            raise SynapseError(
+                400, "Cannot send m.room.aliases events via /rooms/{room_id}/send"
+            )
+
         event_dict = {
             "type": event_type,
             "content": content,
diff --git a/tests/rest/admin/test_admin.py b/tests/rest/admin/test_admin.py
index 0342aed41..e5984aaad 100644
--- a/tests/rest/admin/test_admin.py
+++ b/tests/rest/admin/test_admin.py
@@ -868,13 +868,6 @@ class RoomTestCase(unittest.HomeserverTestCase):
         self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
 
         # Set this new alias as the canonical alias for this room
-        self.helper.send_state(
-            room_id,
-            "m.room.aliases",
-            {"aliases": [test_alias]},
-            tok=self.admin_user_tok,
-            state_key="test",
-        )
         self.helper.send_state(
             room_id,
             "m.room.canonical_alias",
diff --git a/tests/rest/client/v1/test_directory.py b/tests/rest/client/v1/test_directory.py
index 633b7dbda..914cf5492 100644
--- a/tests/rest/client/v1/test_directory.py
+++ b/tests/rest/client/v1/test_directory.py
@@ -51,26 +51,30 @@ class DirectoryTestCase(unittest.HomeserverTestCase):
         self.user = self.register_user("user", "test")
         self.user_tok = self.login("user", "test")
 
-    def test_state_event_not_in_room(self):
-        self.ensure_user_left_room()
-        self.set_alias_via_state_event(403)
+    def test_cannot_set_alias_via_state_event(self):
+        self.ensure_user_joined_room()
+        url = "/_matrix/client/r0/rooms/%s/state/m.room.aliases/%s" % (
+            self.room_id,
+            self.hs.hostname,
+        )
+
+        data = {"aliases": [self.random_alias(5)]}
+        request_data = json.dumps(data)
+
+        request, channel = self.make_request(
+            "PUT", url, request_data, access_token=self.user_tok
+        )
+        self.render(request)
+        self.assertEqual(channel.code, 400, channel.result)
 
     def test_directory_endpoint_not_in_room(self):
         self.ensure_user_left_room()
         self.set_alias_via_directory(403)
 
-    def test_state_event_in_room_too_long(self):
-        self.ensure_user_joined_room()
-        self.set_alias_via_state_event(400, alias_length=256)
-
     def test_directory_in_room_too_long(self):
         self.ensure_user_joined_room()
         self.set_alias_via_directory(400, alias_length=256)
 
-    def test_state_event_in_room(self):
-        self.ensure_user_joined_room()
-        self.set_alias_via_state_event(200)
-
     def test_directory_in_room(self):
         self.ensure_user_joined_room()
         self.set_alias_via_directory(200)
@@ -102,21 +106,6 @@ class DirectoryTestCase(unittest.HomeserverTestCase):
         self.render(request)
         self.assertEqual(channel.code, 200, channel.result)
 
-    def set_alias_via_state_event(self, expected_code, alias_length=5):
-        url = "/_matrix/client/r0/rooms/%s/state/m.room.aliases/%s" % (
-            self.room_id,
-            self.hs.hostname,
-        )
-
-        data = {"aliases": [self.random_alias(alias_length)]}
-        request_data = json.dumps(data)
-
-        request, channel = self.make_request(
-            "PUT", url, request_data, access_token=self.user_tok
-        )
-        self.render(request)
-        self.assertEqual(channel.code, expected_code, channel.result)
-
     def set_alias_via_directory(self, expected_code, alias_length=5):
         url = "/_matrix/client/r0/directory/room/%s" % self.random_alias(alias_length)
         data = {"room_id": self.room_id}