diff --git a/zerver/lib/actions.py b/zerver/lib/actions.py
index 675850684e..49d0e223e0 100644
--- a/zerver/lib/actions.py
+++ b/zerver/lib/actions.py
@@ -4114,7 +4114,7 @@ def do_change_plan_type(
 
 
 def do_change_default_sending_stream(
-    user_profile: UserProfile, stream: Optional[Stream], acting_user: Optional[UserProfile] = None
+    user_profile: UserProfile, stream: Optional[Stream], *, acting_user: Optional[UserProfile]
 ) -> None:
     old_value = user_profile.default_sending_stream_id
     user_profile.default_sending_stream = stream
diff --git a/zerver/tests/test_events.py b/zerver/tests/test_events.py
index c85907b8c3..825c4796f4 100644
--- a/zerver/tests/test_events.py
+++ b/zerver/tests/test_events.py
@@ -1462,11 +1462,11 @@ class NormalActionsTest(BaseAction):
         bot = self.create_bot("test")
         stream = get_stream("Rome", bot.realm)
 
-        action = lambda: do_change_default_sending_stream(bot, stream)
+        action = lambda: do_change_default_sending_stream(bot, stream, acting_user=None)
         events = self.verify_action(action)
         check_realm_bot_update("events[0]", events[0], "default_sending_stream")
 
-        action = lambda: do_change_default_sending_stream(bot, None)
+        action = lambda: do_change_default_sending_stream(bot, None, acting_user=None)
         events = self.verify_action(action)
         check_realm_bot_update("events[0]", events[0], "default_sending_stream")