diff --git a/src/optflow/optflow-demo.cpp b/src/optflow/optflow-demo.cpp
index 7f15a6a5b..c85dba10a 100644
--- a/src/optflow/optflow-demo.cpp
+++ b/src/optflow/optflow-demo.cpp
@@ -154,7 +154,7 @@ bool detect_scene_change(const cv::UMat& srcMotionMaskGrey, const float thresh,
     return result;
 }
 
-void visualize_sparse_optical_flow(const cv::UMat &prevGrey, const cv::UMat &nextGrey, vector<cv::Point2f> &detectedPoints, const float scaleFactor, const int maxStrokeSize, const cv::Scalar color, const int maxPoints, const float pointLossPercent) {
+void visualize_sparse_optical_flow(const cv::UMat &prevGrey, const cv::UMat &nextGrey, const vector<cv::Point2f> &detectedPoints, const float scaleFactor, const int maxStrokeSize, const cv::Scalar color, const int maxPoints, const float pointLossPercent) {
     static vector<cv::Point2f> hull, prevPoints, nextPoints, newPoints;
     static vector<cv::Point2f> upPrevPoints, upNextPoints;
     static std::vector<uchar> status;