diff --git a/libs/utils/energy_model.py b/libs/utils/energy_model.py
index d5fbb2ec9cb6ac48e4bd689b8c416a404516f1cf..7517dd24c69a9bb0dcdf0811b386bcd6e19dfed2 100644
--- a/libs/utils/energy_model.py
+++ b/libs/utils/energy_model.py
@@ -192,13 +192,18 @@ class PowerDomain(_CpuTree):
                         not store power data - these names are used as keys into
                         the ``idle_states`` field of :class:`EnergyModelNode`
                         objects.
+    :type idle_states: list(str)
     :param cpu: The CPU this node represents. If provided, this is a leaf node.
+    :type cpu:  int
     :param children: Non-empty list of child :class:`PowerDomain` objects
+    :type children:  list(PowerDomain)
 
     :ivar cpus: CPUs contained in this node. Includes those of child nodes.
     :type cpus: tuple(int)
     """
     def __init__(self, idle_states, cpu=None, children=None):
+        if idle_states is None:
+            raise ValueError('idle_states cannot be None (but may be empty)')
         super(PowerDomain, self).__init__(cpu, children)
         self.idle_states = idle_states