diff --git a/taiga/timeline/serializers.py b/taiga/timeline/serializers.py
index 6bc428bf..fb914c24 100644
--- a/taiga/timeline/serializers.py
+++ b/taiga/timeline/serializers.py
@@ -18,10 +18,12 @@
 from urllib.parse import urlparse
 
 from django.core.files.storage import default_storage
+from django.conf import settings
 from django.contrib.auth import get_user_model
 
 from taiga.base.api import serializers
 from taiga.base.fields import Field, MethodField
+from taiga.base.utils.thumbnails import get_thumbnail_url
 from taiga.users.services import get_user_photo_url, get_user_big_photo_url
 from taiga.users.gravatar import get_user_gravatar_id
 
@@ -77,8 +79,13 @@ class TimelineSerializer(serializers.LightSerializer):
         if 'attached_file' in item:
             attached_file = item['attached_file']
         else:
+            # This is the case for old timeline entries
             file_path = urlparse(item['url']).path
             index = file_path.find('/attachments')
             attached_file = file_path[index+1:]
 
         item['url'] = default_storage.url(attached_file)
+        thumb_url = get_thumbnail_url(attached_file,
+                                      settings.THN_ATTACHMENT_TIMELINE)
+
+        item['thumb_url'] = thumb_url