diff --git a/modoboa/extensions/webmail/lib.py b/modoboa/extensions/webmail/lib.py
index 91fa0a798..878d35070 100644
--- a/modoboa/extensions/webmail/lib.py
+++ b/modoboa/extensions/webmail/lib.py
@@ -293,7 +293,7 @@ class ImapEmail(Email):
                 continue
             fname = "webmail/%s_%s" % (self.mailid, cid)
             path = os.path.join(settings.MEDIA_ROOT, fname)
-            params["fname"] = settings.MEDIA_URL+"/%s" % fname
+            params["fname"] = os.path.join(settings.MEDIA_URL, fname)
             if os.path.exists(path):
                 continue