diff --git a/FDTD/operator.cpp b/FDTD/operator.cpp
index 641ef53..8314cb6 100644
--- a/FDTD/operator.cpp
+++ b/FDTD/operator.cpp
@@ -102,14 +102,14 @@ unsigned int Operator::CalcNyquistNum(double fmax)
 	return floor(T0/2/dT);
 }
 
-double Operator::GetMeshDelta(int n, unsigned int* pos, bool dualMesh) const
+double Operator::GetMeshDelta(int n, const unsigned int* pos, bool dualMesh) const
 {
 	if ((n<0) || (n>2)) return 0.0;
 	int i_pos[] = {pos[0],pos[1],pos[2]};
 	return GetMeshDelta(n,i_pos,dualMesh);
 }
 
-double Operator::GetMeshDelta(int n, int* pos, bool dualMesh) const
+double Operator::GetMeshDelta(int n, const int* pos, bool dualMesh) const
 {
 	if ((n<0) || (n>2)) return 0.0;
 	if (dualMesh==false)
diff --git a/FDTD/operator.h b/FDTD/operator.h
index c4fd927..ee1a9b4 100644
--- a/FDTD/operator.h
+++ b/FDTD/operator.h
@@ -69,8 +69,8 @@ public:
 
 	virtual double GetGridDelta() const {return gridDelta;}
 	//! Get the mesh delta times the grid delta for a 3D position
-	virtual double GetMeshDelta(int n, int* pos, bool dualMesh=false) const;
-	virtual double GetMeshDelta(int n, unsigned int* pos, bool dualMesh=false) const;
+	virtual double GetMeshDelta(int n, const int* pos, bool dualMesh=false) const;
+	virtual double GetMeshDelta(int n, const unsigned int* pos, bool dualMesh=false) const;
 
 	//! Get the disc line in n direction
 	virtual double GetDiscLine(int n, int pos, bool dualMesh=false) const;