diff --git a/hpvm/include/SupportVISC/DFGraph.h b/hpvm/include/SupportVISC/DFGraph.h
index 677b5f860d6f1b91cff4b12b9be83c15950c83db..a5d7252f4050d0cbc3adc36c17e05d9220f2e57a 100644
--- a/hpvm/include/SupportVISC/DFGraph.h
+++ b/hpvm/include/SupportVISC/DFGraph.h
@@ -313,7 +313,7 @@ public:
       DFInternalNode* _Parent, unsigned _NumOfDim, std::vector<Value*>
       _DimLimits, DFNodeKind _K);
 
-  bool isRoot() {
+  bool isRoot() const {
     // It is a root node is it was created from a launch intrinsic
     return II->getCalledFunction()->getName().equals("llvm.visc.launch");
   }