diff --git a/exp/gocv-exp/main.go b/exp/gocv-exp/main.go
index 4cbcf6a8..086390c7 100644
--- a/exp/gocv-exp/main.go
+++ b/exp/gocv-exp/main.go
@@ -1,3 +1,4 @@
+//go:build !nocv
 // +build !nocv
 
 // What it does:
@@ -93,8 +94,8 @@ func main() {
 
 		// now find contours
 		contours := gocv.FindContours(imgThresh, gocv.RetrievalExternal, gocv.ChainApproxSimple)
-		for _, c := range contours {
-			area := gocv.ContourArea(c)
+		for i := 0; i < contours.Size(); i++ {
+			area := gocv.ContourArea(contours.At(i))
 			if area < float64(minArea) {
 				continue
 			}
@@ -104,7 +105,7 @@ func main() {
 
 			//gocv.DrawContours(&img, contours, i, statusColor, 2)
 
-			rect := gocv.BoundingRect(c)
+			rect := gocv.BoundingRect(contours.At(i))
 			gocv.Rectangle(&img, rect, color.RGBA{0, 0, 255, 0}, 1)
 		}
 
diff --git a/filter/knn.go b/filter/knn.go
index abc8eb83..18b612e4 100644
--- a/filter/knn.go
+++ b/filter/knn.go
@@ -1,3 +1,4 @@
+//go:build !nocv
 // +build !nocv
 
 /*
@@ -117,9 +118,9 @@ func (m *KNN) Detect(img *gocv.Mat) bool {
 	// Find contours and reject ones with a small area.
 	var contours [][]image.Point
 	allContours := gocv.FindContours(imgDelta, gocv.RetrievalExternal, gocv.ChainApproxSimple)
-	for _, c := range allContours {
-		if gocv.ContourArea(c) > m.area {
-			contours = append(contours, c)
+	for i := 0; i < allContours.Size(); i++ {
+		if gocv.ContourArea(allContours.At(i)) > m.area {
+			contours = append(contours, allContours.At(i).ToPoints())
 		}
 	}
 
diff --git a/filter/mog.go b/filter/mog.go
index f7ef6dbd..c3b15a93 100644
--- a/filter/mog.go
+++ b/filter/mog.go
@@ -1,3 +1,4 @@
+//go:build !nocv
 // +build !nocv
 
 /*
@@ -117,9 +118,10 @@ func (m *MOG) Detect(img *gocv.Mat) bool {
 	// Find contours and reject ones with a small area.
 	var contours [][]image.Point
 	allContours := gocv.FindContours(imgDelta, gocv.RetrievalExternal, gocv.ChainApproxSimple)
-	for _, c := range allContours {
-		if gocv.ContourArea(c) > m.area {
-			contours = append(contours, c)
+
+	for i := 0; i < allContours.Size(); i++ {
+		if gocv.ContourArea(allContours.At(i)) > m.area {
+			contours = append(contours, allContours.At(i).ToPoints())
 		}
 	}