diff --git a/seahub/thumbnail/utils.py b/seahub/thumbnail/utils.py
index 81f90c1fe4..3c0b1b0229 100644
--- a/seahub/thumbnail/utils.py
+++ b/seahub/thumbnail/utils.py
@@ -1,5 +1,5 @@
-import os
+import posixpath
 from seahub.utils import get_service_url
 def get_thumbnail_src(repo_id, obj_id, size):
-    return os.path.join(get_service_url(), "thumbnail", repo_id,
-                        obj_id, size, '')
+    return posixpath.join(get_service_url(), "thumbnail", repo_id,
+                          obj_id, size)