diff --git a/docs/configuration.rst b/docs/configuration.rst
index 85229668..932b736f 100644
--- a/docs/configuration.rst
+++ b/docs/configuration.rst
@@ -2703,6 +2703,8 @@ Description
     for each Tweet in said timeline.
 
     Note: This requires at least 1 additional API call per initial Tweet.
+    Age-restricted replies cannot be expanded when using the
+    `syndication <extractor.twitter.syndication_>`__ API.
 
 
 extractor.twitter.size
diff --git a/gallery_dl/extractor/twitter.py b/gallery_dl/extractor/twitter.py
index 712e9ddb..020b57cc 100644
--- a/gallery_dl/extractor/twitter.py
+++ b/gallery_dl/extractor/twitter.py
@@ -365,18 +365,22 @@ class TwitterExtractor(Extractor):
     def _expand_tweets(self, tweets):
         seen = set()
         for tweet in tweets:
-
-            if "legacy" in tweet:
-                cid = tweet["legacy"]["conversation_id_str"]
-            else:
-                cid = tweet["conversation_id_str"]
-
-            if cid not in seen:
-                seen.add(cid)
-                try:
-                    yield from self.api.tweet_detail(cid)
-                except Exception:
-                    yield tweet
+            obj = tweet["legacy"] if "legacy" in tweet else tweet
+            cid = obj.get("conversation_id_str")
+            if not cid:
+                tid = obj["id_str"]
+                self.log.warning(
+                    "Unable to expand %s (no 'conversation_id')", tid)
+                continue
+            if cid in seen:
+                self.log.debug(
+                    "Skipping expansion of %s (previously seen)", cid)
+                continue
+            seen.add(cid)
+            try:
+                yield from self.api.tweet_detail(cid)
+            except Exception:
+                yield tweet
 
     def _make_tweet(self, user, id_str, url, timestamp):
         return {
@@ -1520,6 +1524,12 @@ class TwitterAPI():
         else:
             retweet_id = None
 
+        # assume 'conversation_id' is the same as 'id' when the tweet
+        # is not a reply
+        if "conversation_id_str" not in tweet and \
+                "in_reply_to_status_id_str" not in tweet:
+            tweet["conversation_id_str"] = tweet["id_str"]
+
         tweet["created_at"] = text.parse_datetime(
             tweet["created_at"], "%Y-%m-%dT%H:%M:%S.%fZ").strftime(
             "%a %b %d %H:%M:%S +0000 %Y")