diff --git a/include/sta/Bdd.hh b/include/sta/Bdd.hh
index e34a7bd7..b0497d25 100644
--- a/include/sta/Bdd.hh
+++ b/include/sta/Bdd.hh
@@ -34,7 +34,7 @@ struct DdManager;
 
 namespace sta {
 
-typedef std::map<const LibertyPort*, DdNode*> BddPortVarMap;
+typedef std::map<const LibertyPort*, DdNode*, LibertyPortLess> BddPortVarMap;
 typedef std::map<unsigned, const LibertyPort*> BddVarIdxPortMap;
 
 class Bdd : public StaState
diff --git a/include/sta/LibertyClass.hh b/include/sta/LibertyClass.hh
index b28d0765..06f2729f 100644
--- a/include/sta/LibertyClass.hh
+++ b/include/sta/LibertyClass.hh
@@ -145,6 +145,12 @@ enum class TableAxisVariable {
 enum class PathType { clk, data, clk_and_data };
 const int path_type_count = 2;
 
+class LibertyPortLess
+{
+public:
+  bool operator()(const LibertyPort *port1, const LibertyPort *port2) const;
+};
+
 class LibertyPortNameLess
 {
 public:
diff --git a/liberty/Liberty.cc b/liberty/Liberty.cc
index 9eeb9536..5a05c424 100644
--- a/liberty/Liberty.cc
+++ b/liberty/Liberty.cc
@@ -2833,6 +2833,13 @@ sortByName(const LibertyPortSet *set)
   return ports;
 }
 
+bool
+LibertyPortLess::operator()(const LibertyPort *port1,
+                            const LibertyPort *port2) const
+{
+  return LibertyPort::less(port1, port2);
+}
+
 bool
 LibertyPortNameLess::operator()(const LibertyPort *port1,
 				const LibertyPort *port2) const