diff --git a/EGkCAvToolSurfTm.h b/EGkCAvToolSurfTm.h
index 176ea05..0a7a43f 100644
--- a/EGkCAvToolSurfTm.h
+++ b/EGkCAvToolSurfTm.h
@@ -38,7 +38,7 @@ class __declspec( novtable) ICAvToolSurfTm {
       virtual double GetToolRadius( void) const = 0 ;
       virtual double GetToolHeight( void) const = 0 ;
       virtual const ICurveComposite& GetToolOutline( bool bApprox = false) const = 0 ;
-      virtual bool TestPosition( const Point3d& ptT, const Vector3d& vtDir, const Vector3d& vtMove, double& dTotDist) = 0 ;
+      virtual bool TestPosition( const Point3d& ptT, const Vector3d& vtDir, const Vector3d& vtMove, double& dTotDist) const = 0 ;
       virtual bool TestSeries( PNTUVECTOR& vPntM, const Vector3d& vtDir, const Vector3d& vtMove, double dProgCoeff = 1) = 0 ;
       virtual bool TestPath( PNTULIST& lPntM, const Vector3d& vtDir, const Vector3d& vtMove, double dLinTol, double dProgCoeff = 1) = 0 ;
 } ;