diff --git a/hpvm/include/SupportVISC/DFGraph.h b/hpvm/include/SupportVISC/DFGraph.h
index 160e65928463d59ae51461959b473175cdb4a090..de0f5f9945038287b671642e385d5d466e466bce 100644
--- a/hpvm/include/SupportVISC/DFGraph.h
+++ b/hpvm/include/SupportVISC/DFGraph.h
@@ -103,11 +103,11 @@ public:
     return Exit;
   }
 
-  bool isEntry(DFNode* N) const {
+  bool isEntry(const DFNode* N) const {
     return N == Entry;
   }
 
-  bool isExit(DFNode* N) const {
+  bool isExit(const DFNode* N) const {
     return N == Exit;
   }
 
@@ -576,7 +576,7 @@ public:
     return Hint;
   }
 
-  bool isDummyNode() {
+  bool isDummyNode() const {
     return isEntryNode() || isExitNode();
   }
 
@@ -585,8 +585,8 @@ public:
     return PropertyList.count(Allocation) != 0;
   }
   void setRank(unsigned r);
-  bool isEntryNode();
-  bool isExitNode();
+  bool isEntryNode() const;
+  bool isExitNode() const;
   DFEdge* getInDFEdgeAt(unsigned inPort);
   DFEdge* getExtendedInDFEdgeAt(unsigned inPort);
   DFEdge* getOutDFEdgeAt(unsigned outPort);
@@ -865,13 +865,13 @@ void DFNode::setRank(unsigned r) {
   }
 }
 
-bool DFNode::isEntryNode() {
+bool DFNode::isEntryNode() const {
   if (Parent == NULL)
     return false;
   return Parent->getChildGraph()->isEntry(this);
 }
 
-bool DFNode::isExitNode() {
+bool DFNode::isExitNode() const {
   if (Parent == NULL)
     return false;
   return Parent->getChildGraph()->isExit(this);