diff --git a/inbox.py b/inbox.py
index a01d73764..c077ed2cf 100644
--- a/inbox.py
+++ b/inbox.py
@@ -18,6 +18,7 @@ from languages import understood_post_language
 from like import update_likes_collection
 from reaction import update_reaction_collection
 from reaction import valid_emoji_content
+from utils import contains_invalid_actor_url_chars
 from utils import is_quote_toot
 from utils import acct_handle_dir
 from utils import is_account_dir
@@ -2756,14 +2757,17 @@ def _receive_announce(recent_posts_cache: {},
         # so that their avatar can be shown
         lookup_actor = None
         if post_json_object.get('attributedTo'):
-            if isinstance(post_json_object['attributedTo'], str):
-                lookup_actor = post_json_object['attributedTo']
+            attrib = post_json_object['attributedTo']
+            if isinstance(attrib, str):
+                if not contains_invalid_actor_url_chars(attrib):
+                    lookup_actor = attrib
         else:
             if has_object_dict(post_json_object):
                 if post_json_object['object'].get('attributedTo'):
                     attrib = post_json_object['object']['attributedTo']
                     if isinstance(attrib, str):
-                        lookup_actor = attrib
+                        if not contains_invalid_actor_url_chars(attrib):
+                            lookup_actor = attrib
         if lookup_actor:
             if has_users_path(lookup_actor):
                 if '/statuses/' in lookup_actor:
diff --git a/outbox.py b/outbox.py
index f603d450f..2a557db43 100644
--- a/outbox.py
+++ b/outbox.py
@@ -15,6 +15,7 @@ from posts import outbox_message_create_wrap
 from posts import save_post_to_box
 from posts import send_to_followers_thread
 from posts import send_to_named_addresses_thread
+from utils import contains_invalid_actor_url_chars
 from utils import get_attachment_property_value
 from utils import get_account_timezone
 from utils import has_object_string_type
@@ -321,6 +322,9 @@ def post_message_to_outbox(session, translate: {},
            '.' not in message_json['actor']:
             return False
 
+        if contains_invalid_actor_url_chars(message_json['actor']):
+            return False
+
         # sent by an actor on a local network address?
         if not allow_local_network_access:
             local_network_pattern_list = get_local_network_addresses()