diff --git a/qutebrowser/misc/sessions.py b/qutebrowser/misc/sessions.py
index b94566830..e50d803a2 100644
--- a/qutebrowser/misc/sessions.py
+++ b/qutebrowser/misc/sessions.py
@@ -40,6 +40,8 @@ from qutebrowser.qt import sip
 
 class Sentinel:
 
+    """Sentinel value for default argument."""
+
     pass