diff --git a/zerver/lib/actions.py b/zerver/lib/actions.py
index 99549953a4..d6c67ec716 100644
--- a/zerver/lib/actions.py
+++ b/zerver/lib/actions.py
@@ -1842,7 +1842,7 @@ def get_recipient_from_user_ids(recipient_profile_ids: Set[int],
     else:
         return get_personal_recipient(list(recipient_profile_ids)[0])
 
-def validate_recipient_user_profiles(user_profiles: List[UserProfile],
+def validate_recipient_user_profiles(user_profiles: Sequence[UserProfile],
                                      sender: UserProfile,
                                      allow_deactivated: bool=False) -> Set[int]:
     recipient_profile_ids = set()
@@ -1904,7 +1904,7 @@ def recipient_for_user_ids(user_ids: Iterable[int], sender: UserProfile) -> Reci
         sender=sender
     )
 
-def recipient_for_user_profiles(user_profiles: List[UserProfile], forwarded_mirror_message: bool,
+def recipient_for_user_profiles(user_profiles: Sequence[UserProfile], forwarded_mirror_message: bool,
                                 forwarder_user_profile: Optional[UserProfile],
                                 sender: UserProfile, allow_deactivated: bool=False) -> Recipient:
 
diff --git a/zerver/lib/addressee.py b/zerver/lib/addressee.py
index 903aa63d30..d969311e7b 100644
--- a/zerver/lib/addressee.py
+++ b/zerver/lib/addressee.py
@@ -91,9 +91,10 @@ class Addressee:
     def is_private(self) -> bool:
         return self._msg_type == 'private'
 
-    def user_profiles(self) -> List[UserProfile]:
+    def user_profiles(self) -> Sequence[UserProfile]:
         assert(self.is_private())
-        return self._user_profiles  # type: ignore # assertion protects us
+        assert self._user_profiles is not None
+        return self._user_profiles
 
     def stream(self) -> Optional[Stream]:
         assert(self.is_stream())