diff --git a/synapse/config/server.py b/synapse/config/server.py
index 6b299836176..3b2947d29e1 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -794,6 +794,8 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         else:
             self.max_event_delay_ms = None
 
+        self.account_data_defaults = config.get("account_data_defaults", {})
+
     def has_tls_listener(self) -> bool:
         return any(listener.is_tls() for listener in self.listeners)
 
diff --git a/synapse/rest/client/account_data.py b/synapse/rest/client/account_data.py
index 734c9e992f5..5088b73d378 100644
--- a/synapse/rest/client/account_data.py
+++ b/synapse/rest/client/account_data.py
@@ -116,9 +116,6 @@ async def on_GET(
                 user_id, account_data_type
             )
 
-        if account_data is None:
-            raise NotFoundError("Account data not found")
-
         # If experimental support for MSC3391 is enabled, then this endpoint should
         # return a 404 if the content for an account data type is an empty dict.
         if self._hs.config.experimental.msc3391_enabled and account_data == {}:
diff --git a/synapse/storage/databases/main/account_data.py b/synapse/storage/databases/main/account_data.py
index e583c182bad..557e0b61d08 100644
--- a/synapse/storage/databases/main/account_data.py
+++ b/synapse/storage/databases/main/account_data.py
@@ -102,6 +102,8 @@ def __init__(
             self._delete_account_data_for_deactivated_users,
         )
 
+        self.defaults = hs.config.server.account_data_defaults
+
     def get_max_account_data_stream_id(self) -> int:
         """Get the current max stream ID for account data stream
 
@@ -149,11 +151,17 @@ def get_global_account_data_for_user(
 
             txn.execute(sql, (user_id,))
 
-            return {
+            user_account_data = {
                 account_data_type: db_to_json(content)
                 for account_data_type, content in txn
             }
 
+            for type, content in self.defaults.items():
+                if user_account_data.get(type) is None:
+                    user_account_data[type] = content
+
+            return user_account_data
+
         return await self.db_pool.runInteraction(
             "get_global_account_data_for_user", get_global_account_data_for_user
         )
@@ -225,7 +233,7 @@ async def get_global_account_data_by_type_for_user(
         if result:
             return db_to_json(result)
         else:
-            return None
+            return self.defaults.get(data_type)
 
     async def get_latest_stream_id_for_global_account_data_by_type_for_user(
         self, user_id: str, data_type: str