diff --git a/power/Power.cc b/power/Power.cc
index 8a9aed76..3265fe96 100644
--- a/power/Power.cc
+++ b/power/Power.cc
@@ -101,6 +101,7 @@ Power::Power(StaState *sta) :
   seq_activity_map_(100, SeqPinHash(network_), SeqPinEqual()),
   activities_valid_(false),
   bdd_(sta),
+  instance_powers_(InstanceIdLess(network_)),
   instance_powers_valid_(false),
   corner_(nullptr)
 {
diff --git a/power/Power.hh b/power/Power.hh
index 5c45fd60..abed2f40 100644
--- a/power/Power.hh
+++ b/power/Power.hh
@@ -238,7 +238,7 @@ private:
   PwrSeqActivityMap seq_activity_map_;
   bool activities_valid_;
   Bdd bdd_;
-  std::map<const Instance*, PowerResult> instance_powers_;
+  std::map<const Instance*, PowerResult, InstanceIdLess> instance_powers_;
   bool instance_powers_valid_;
   const Corner *corner_;