diff --git a/activitypub.py b/activitypub.py
index d6c122d..f45aad9 100644
--- a/activitypub.py
+++ b/activitypub.py
@@ -367,14 +367,14 @@ class MicroblogPubBackend(Backend):
         )
 
         logger.info(f"inbox_delete handle_replies obj={obj!r}")
-        in_reply_to = obj.inReplyTo
+        in_reply_to = obj.get_in_reply_to()
         if delete.get_object().ACTIVITY_TYPE != ap.ActivityType.NOTE:
-            in_reply_to = DB.activities.find_one(
+            in_reply_to = ap._get_id(DB.activities.find_one(
                 {
                     "activity.object.id": delete.get_object().id,
                     "type": ap.ActivityType.CREATE.value,
                 }
-            )["activity"]["object"].get("inReplyTo")
+            )["activity"]["object"].get("inReplyTo"))
 
         # Fake a Undo so any related Like/Announce doesn't appear on the web UI
         DB.activities.update(
@@ -406,7 +406,7 @@ class MicroblogPubBackend(Backend):
             {"$set": {"meta.undo": True, "meta.exta": "object deleted"}},
         )
 
-        self._handle_replies_delete(as_actor, obj.inReplyTo)
+        self._handle_replies_delete(as_actor, obj.get_in_reply_to())
 
     @ensure_it_is_me
     def inbox_update(self, as_actor: ap.Person, update: ap.Update) -> None:
@@ -524,7 +524,7 @@ class MicroblogPubBackend(Backend):
     def _handle_replies(self, as_actor: ap.Person, create: ap.Create) -> None:
         """Go up to the root reply, store unknown replies in the `threads` DB and set the "meta.thread_root_parent"
         key to make it easy to query a whole thread."""
-        in_reply_to = create.get_object().inReplyTo
+        in_reply_to = create.get_object().get_in_reply_to()
         if not in_reply_to:
             return
 
@@ -563,7 +563,7 @@ class MicroblogPubBackend(Backend):
             # TODO(tsileo): parses the replies collection and import the replies?
 
         while reply is not None:
-            in_reply_to = reply.inReplyTo
+            in_reply_to = reply.get_in_reply_to()
             if not in_reply_to:
                 break
             root_reply = in_reply_to
diff --git a/app.py b/app.py
index 15f20dd..27e47dd 100644
--- a/app.py
+++ b/app.py
@@ -901,7 +901,7 @@ def _build_thread(data, include_children=True):  # noqa: C901
         rep_id = rep["activity"]["object"]["id"]
         if rep_id == root_id:
             continue
-        reply_of = rep["activity"]["object"]["inReplyTo"]
+        reply_of = ap._get_id(rep["activity"]["object"]["inReplyTo"])
         try:
             idx[reply_of]["_nodes"].append(rep)
         except KeyError:
@@ -2544,7 +2544,8 @@ def invalidate_cache(activity):
         DB.cache2.remove()
     elif activity.has_type(ap.ActivityType.CREATE):
         note = activity.get_object()
-        if not note.inReplyTo or note.inReplyTo.startswith(ID):
+        in_reply_to = note.get_in_reply_to()
+        if not in_reply_to or in_reply_to.startswith(ID):
             DB.cache2.remove()
         # FIXME(tsileo): check if it's a reply of a reply
 
@@ -2696,19 +2697,20 @@ def task_process_new_activity():
 
         elif activity.has_type(ap.ActivityType.CREATE):
             note = activity.get_object()
+            in_reply_to = note.get_in_reply_to()
             # Make the note part of the stream if it's not a reply, or if it's a local reply
-            if not note.inReplyTo or note.inReplyTo.startswith(ID):
+            if not in_reply_to or in_reply_to.startswith(ID):
                 tag_stream = True
 
             # FIXME(tsileo): check for direct addressing in the to, cc, bcc... fields
-            if (note.inReplyTo and note.inReplyTo.startswith(ID)) or note.has_mention(
+            if (in_reply_to and in_reply_to.startswith(ID)) or note.has_mention(
                 ID
             ):
                 should_keep = True
 
-            if note.inReplyTo:
+            if in_reply_to:
                 try:
-                    reply = ap.fetch_remote_activity(note.inReplyTo)
+                    reply = ap.fetch_remote_activity(note.get_in_reply_to())
                     if (
                         reply.id.startswith(ID) or reply.has_mention(ID)
                     ) and activity.is_public():
@@ -2731,7 +2733,7 @@ def task_process_new_activity():
                         should_forward = True
 
             # [X] The values of inReplyTo, object, target and/or tag are objects owned by the server
-            if not (note.inReplyTo and note.inReplyTo.startswith(ID)):
+            if not (in_reply_to and in_reply_to.startswith(ID)):
                 should_forward = False
 
         elif activity.has_type(ap.ActivityType.DELETE):