diff --git a/synapse/storage/databases/main/account_data.py b/synapse/storage/databases/main/account_data.py
index 0df12e6380..96e1e5e45b 100644
--- a/synapse/storage/databases/main/account_data.py
+++ b/synapse/storage/databases/main/account_data.py
@@ -469,9 +469,9 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
 
         content_json = json_encoder.encode(content)
 
-        async with self._account_data_id_gen.get_next() as next_id:
-            await self.db_pool.simple_upsert(
-                desc="add_room_account_data",
+        def _add_account_data_to_room(txn: LoggingTransaction, next_id: int) -> None:
+            self.db_pool.simple_upsert_txn(
+                txn,
                 table="room_account_data",
                 keyvalues={
                     "user_id": user_id,
@@ -481,6 +481,18 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
                 values={"stream_id": next_id, "content": content_json},
             )
 
+            # Clear any previous record that this user account data type was deleted.
+            self._remove_entries_from_account_data_undelivered_deletes_for_type_txn(
+                txn, account_data_type, room_id, user_id
+            )
+
+        async with self._account_data_id_gen.get_next() as next_id:
+            await self.db_pool.runInteraction(
+                "add_account_data_to_room",
+                _add_account_data_to_room,
+                next_id,
+            )
+
             self._account_data_stream_cache.entity_has_changed(user_id, next_id)
             self.get_account_data_for_user.invalidate((user_id,))
             self.get_account_data_for_room.invalidate((user_id, room_id))
@@ -620,6 +632,11 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
             values={"stream_id": next_id, "content": content_json},
         )
 
+        # Clear any previous record that this user account data type was deleted.
+        self._remove_entries_from_account_data_undelivered_deletes_for_type_txn(
+            txn, account_data_type, room_id=None, user_id=user_id
+        )
+
         # Ignored users get denormalized into a separate table as an optimisation.
         if account_data_type != AccountDataTypes.IGNORED_USER_LIST:
             return
@@ -821,6 +838,40 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
             ),
         )
 
+    def _remove_entries_from_account_data_undelivered_deletes_for_type_txn(
+        self,
+        txn: LoggingTransaction,
+        account_data_type: str,
+        room_id: Optional[str],
+        user_id: str,
+    ) -> None:
+        """
+        Removes all entries from the 'account_data_undelivered_deletes' table for a given
+        {user,room} account data entry.
+
+        This should be called when adding/updating an account data entry, as the entry
+        will no longer be in a deleted state.
+
+        Args:
+            txn: The transaction that is handling the addition/modification to the
+                relevant account data type.
+            account_data_type: The type of {room,user} account data that was modified.
+            room_id: The ID of the room if this refers to room account data, otherwise
+                this should be None.
+            user_id: The ID of the user this account data is related to.
+        """
+        # Remove all entries pertaining to this account data type as it is
+        # no longer deleted!
+        self.db_pool.simple_delete_txn(
+            txn,
+            table="account_data_undelivered_deletes",
+            keyvalues={
+                "type": account_data_type,
+                "room_id": room_id,
+                "user_id": user_id,
+            },
+        )
+
     async def purge_account_data_for_user(self, user_id: str) -> None:
         """
         Removes ALL the account data for a user.