diff --git a/src/Mod/Robot/App/kdl_cp/trajectory_stationary.hpp b/src/Mod/Robot/App/kdl_cp/trajectory_stationary.hpp
index 27d7b17ce..2dd45fe1f 100644
--- a/src/Mod/Robot/App/kdl_cp/trajectory_stationary.hpp
+++ b/src/Mod/Robot/App/kdl_cp/trajectory_stationary.hpp
@@ -32,7 +32,7 @@ namespace KDL {
 	public:
 		Trajectory_Stationary(double _duration,const Frame& _pos):
 		  pos(_pos),duration(_duration) {}
-		virtual double Duration() {
+		virtual double Duration() const {
 			return duration;
 		}
 		virtual Frame Pos(double time) const {