diff --git a/kwant/system.py b/kwant/system.py
index 9f64c36f3eb909fd33e1c26bc43f25f94920ba16..eca41875c214169f997e5f74df388c034f592e0a 100644
--- a/kwant/system.py
+++ b/kwant/system.py
@@ -58,8 +58,7 @@ class FiniteSystem(System):
     Instance Variables
     ------------------
     leads : sequence of lead objects
-        Each lead object has to provide at least a method
-        ``self_energy(energy)``.
+        Each lead object has to provide a method ``self_energy(energy)``.
     lead_interfaces : sequence of sequences of integers
         Each sub-sequence contains the indices of the system sites to which the
         lead is connected.