diff --git a/changelog.d/10489.feature b/changelog.d/10489.feature
new file mode 100644
index 000000000..df8bb5116
--- /dev/null
+++ b/changelog.d/10489.feature
@@ -0,0 +1 @@
+Update support for [MSC3083](https://github.com/matrix-org/matrix-doc/pull/3083) to consider changes in the MSC around which servers can issue join events.
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index ec96999e4..f4da9e092 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -109,6 +109,8 @@ def prune_event_dict(room_version: RoomVersion, event_dict: dict) -> dict:
         add_fields("creator")
     elif event_type == EventTypes.JoinRules:
         add_fields("join_rule")
+        if room_version.msc3083_join_rules:
+            add_fields("allow")
     elif event_type == EventTypes.PowerLevels:
         add_fields(
             "users",
diff --git a/tests/events/test_utils.py b/tests/events/test_utils.py
index 9274ce4c3..e2a5fc018 100644
--- a/tests/events/test_utils.py
+++ b/tests/events/test_utils.py
@@ -301,6 +301,49 @@ class PruneEventTestCase(unittest.TestCase):
             room_version=RoomVersions.MSC2176,
         )
 
+    def test_join_rules(self):
+        """Join rules events have changed behavior starting with MSC3083."""
+        self.run_test(
+            {
+                "type": "m.room.join_rules",
+                "event_id": "$test:domain",
+                "content": {
+                    "join_rule": "invite",
+                    "allow": [],
+                    "other_key": "stripped",
+                },
+            },
+            {
+                "type": "m.room.join_rules",
+                "event_id": "$test:domain",
+                "content": {"join_rule": "invite"},
+                "signatures": {},
+                "unsigned": {},
+            },
+        )
+
+        # After MSC3083, alias events have no special behavior.
+        self.run_test(
+            {
+                "type": "m.room.join_rules",
+                "content": {
+                    "join_rule": "invite",
+                    "allow": [],
+                    "other_key": "stripped",
+                },
+            },
+            {
+                "type": "m.room.join_rules",
+                "content": {
+                    "join_rule": "invite",
+                    "allow": [],
+                },
+                "signatures": {},
+                "unsigned": {},
+            },
+            room_version=RoomVersions.MSC3083,
+        )
+
 
 class SerializeEventTestCase(unittest.TestCase):
     def serialize(self, ev, fields):