diff --git a/include/sta/NullParasitics.hh b/include/sta/NullParasitics.hh
index 5e49ae6c..21331cb1 100644
--- a/include/sta/NullParasitics.hh
+++ b/include/sta/NullParasitics.hh
@@ -101,8 +101,8 @@ public:
   makeParasiticNetwork(const Net *net,
 		       bool pin_cap_included,
 		       const ParasiticAnalysisPt *ap);
-  virtual ParasiticDeviceIterator *deviceIterator(Parasitic *) { return nullptr; }
-  virtual ParasiticNodeIterator *nodeIterator(Parasitic *) { return nullptr; }
+  virtual ParasiticDeviceIterator *deviceIterator(const Parasitic *) { return nullptr; }
+  virtual ParasiticNodeIterator *nodeIterator(const Parasitic *) { return nullptr; }
   virtual bool includesPinCaps(const Parasitic *parasitic) const;
   virtual void deleteParasiticNetwork(const Net *net,
 				      const ParasiticAnalysisPt *ap);
diff --git a/include/sta/Parasitics.hh b/include/sta/Parasitics.hh
index 8a40a2d7..f7dca806 100644
--- a/include/sta/Parasitics.hh
+++ b/include/sta/Parasitics.hh
@@ -153,8 +153,8 @@ public:
   virtual Parasitic *makeParasiticNetwork(const Net *net,
 					  bool includes_pin_caps,
 					  const ParasiticAnalysisPt *ap) = 0;
-  virtual ParasiticDeviceIterator *deviceIterator(Parasitic *parasitic) = 0;
-  virtual ParasiticNodeIterator *nodeIterator(Parasitic *parasitic) = 0;
+  virtual ParasiticDeviceIterator *deviceIterator(const Parasitic *parasitic) = 0;
+  virtual ParasiticNodeIterator *nodeIterator(const Parasitic *parasitic) = 0;
   // Delete parasitic network if it exists.
   virtual void deleteParasiticNetwork(const Net *net,
 				      const ParasiticAnalysisPt *ap) = 0;
diff --git a/parasitics/ConcreteParasitics.cc b/parasitics/ConcreteParasitics.cc
index 39b40993..2ab1086a 100644
--- a/parasitics/ConcreteParasitics.cc
+++ b/parasitics/ConcreteParasitics.cc
@@ -131,13 +131,13 @@ ConcreteParasitic::setPoleResidue(const Pin *,
 }
 
 ParasiticDeviceIterator *
-ConcreteParasitic::deviceIterator()
+ConcreteParasitic::deviceIterator() const
 {
   return nullptr;
 }
 
 ParasiticNodeIterator *
-ConcreteParasitic::nodeIterator()
+ConcreteParasitic::nodeIterator() const
 {
   return nullptr;
 }
@@ -688,15 +688,15 @@ ConcreteParasiticNetwork::deleteDevices()
 }
 
 ParasiticNodeIterator *
-ConcreteParasiticNetwork::nodeIterator()
+ConcreteParasiticNetwork::nodeIterator() const
 {
   ConcreteParasiticNodeSeq *nodes = new ConcreteParasiticNodeSeq();
-  ConcreteParasiticPinNodeMap::Iterator node_iter2(pin_nodes_);
+  ConcreteParasiticPinNodeMap::ConstIterator node_iter2(pin_nodes_);
   while (node_iter2.hasNext()) {
     ConcreteParasiticPinNode *node = node_iter2.next();
     nodes->push_back(node);
   }
-  ConcreteParasiticSubNodeMap::Iterator node_iter1(sub_nodes_);
+  ConcreteParasiticSubNodeMap::ConstIterator node_iter1(sub_nodes_);
   while (node_iter1.hasNext()) {
     ConcreteParasiticSubNode *node = node_iter1.next();
     nodes->push_back(node);
@@ -705,7 +705,7 @@ ConcreteParasiticNetwork::nodeIterator()
 }
 
 ParasiticDeviceIterator *
-ConcreteParasiticNetwork::deviceIterator()
+ConcreteParasiticNetwork::deviceIterator() const
 {
   ConcreteParasiticDeviceSet *devices1 = new ConcreteParasiticDeviceSet();
   devices(devices1);
@@ -713,11 +713,11 @@ ConcreteParasiticNetwork::deviceIterator()
 }
 
 void
-ConcreteParasiticNetwork::devices(ConcreteParasiticDeviceSet *devices)
+ConcreteParasiticNetwork::devices(ConcreteParasiticDeviceSet *devices) const
 {
   // Collect devices into a set so they are only deleted once
   // because multiple sub-nodes or pin nodes can refer to them.
-  ConcreteParasiticSubNodeMap::Iterator node_iter1(sub_nodes_);
+  ConcreteParasiticSubNodeMap::ConstIterator node_iter1(sub_nodes_);
   while (node_iter1.hasNext()) {
     ConcreteParasiticSubNode *node = node_iter1.next();
     ConcreteParasiticDeviceSeq::Iterator device_iter(node->devices());
@@ -727,10 +727,10 @@ ConcreteParasiticNetwork::devices(ConcreteParasiticDeviceSet *devices)
     }
   }
 
-  ConcreteParasiticPinNodeMap::Iterator node_iter2(pin_nodes_);
+  ConcreteParasiticPinNodeMap::ConstIterator node_iter2(pin_nodes_);
   while (node_iter2.hasNext()) {
     ConcreteParasiticPinNode *node = node_iter2.next();
-    ConcreteParasiticDeviceSeq::Iterator device_iter(node->devices());
+    ConcreteParasiticDeviceSeq::ConstIterator device_iter(node->devices());
     while (device_iter.hasNext()) {
       ConcreteParasiticDevice *device = device_iter.next();
       devices->insert(device);
@@ -1468,16 +1468,16 @@ ConcreteParasitics::makeResistor(const char *name,
 }
 
 ParasiticDeviceIterator *
-ConcreteParasitics::deviceIterator(Parasitic *parasitic)
+ConcreteParasitics::deviceIterator(const Parasitic *parasitic)
 {
-  ConcreteParasitic *cparasitic = static_cast<ConcreteParasitic*>(parasitic);
+  const ConcreteParasitic *cparasitic = static_cast<const ConcreteParasitic*>(parasitic);
   return cparasitic->deviceIterator();
 }
 
 ParasiticNodeIterator *
-ConcreteParasitics::nodeIterator(Parasitic *parasitic)
+ConcreteParasitics::nodeIterator(const Parasitic *parasitic)
 {
-  ConcreteParasitic *cparasitic = static_cast<ConcreteParasitic*>(parasitic);
+  const ConcreteParasitic *cparasitic = static_cast<const ConcreteParasitic*>(parasitic);
   return cparasitic->nodeIterator();
 }
 
diff --git a/parasitics/ConcreteParasitics.hh b/parasitics/ConcreteParasitics.hh
index 45436cb6..c4323c34 100644
--- a/parasitics/ConcreteParasitics.hh
+++ b/parasitics/ConcreteParasitics.hh
@@ -142,8 +142,8 @@ public:
   virtual void makeResistor(const char *name, ParasiticNode *node1,
 			    ParasiticNode *node2,
 			    float res, const ParasiticAnalysisPt *ap);
-  virtual ParasiticDeviceIterator *deviceIterator(Parasitic *parasitic);
-  virtual ParasiticNodeIterator *nodeIterator(Parasitic *parasitic);
+  virtual ParasiticDeviceIterator *deviceIterator(const Parasitic *parasitic);
+  virtual ParasiticNodeIterator *nodeIterator(const Parasitic *parasitic);
 
   virtual const char *name(const ParasiticNode *node);
   virtual const Pin *connectionPin(const ParasiticNode *node) const;
diff --git a/parasitics/ConcreteParasiticsPvt.hh b/parasitics/ConcreteParasiticsPvt.hh
index 93b3f57b..0444b0f6 100644
--- a/parasitics/ConcreteParasiticsPvt.hh
+++ b/parasitics/ConcreteParasiticsPvt.hh
@@ -78,8 +78,8 @@ public:
   virtual void setPoleResidue(const Pin *load_pin,
 			      ComplexFloatSeq *poles,
 			      ComplexFloatSeq *residues);
-  virtual ParasiticDeviceIterator *deviceIterator();
-  virtual ParasiticNodeIterator *nodeIterator();
+  virtual ParasiticDeviceIterator *deviceIterator() const;
+  virtual ParasiticNodeIterator *nodeIterator() const;
 };
 
 // Pi model for a driver pin.
@@ -414,10 +414,10 @@ public:
   ConcreteParasiticSubNodeMap *subNodes() { return &sub_nodes_; }
   void disconnectPin(const Pin *pin,
 		     const Net *net);
-  virtual ParasiticDeviceIterator *deviceIterator();
-  virtual ParasiticNodeIterator *nodeIterator();
+  virtual ParasiticDeviceIterator *deviceIterator() const;
+  virtual ParasiticNodeIterator *nodeIterator() const;
   virtual void devices(// Return value.
-		       ConcreteParasiticDeviceSet *devices);
+		       ConcreteParasiticDeviceSet *devices) const;
 
 private:
   void deleteNodes();