diff --git a/bench/cec2020/helperFunctions.go b/bench/cec2020/helperFunctions.go
index abb8410..2d17ead 100644
--- a/bench/cec2020/helperFunctions.go
+++ b/bench/cec2020/helperFunctions.go
@@ -153,7 +153,7 @@ func getGnx(p []float64, fnx float64) []float64 {
 		gnxsum += gnx[i]
 	}
 
-	gnx[len(p)] = fnx - gnxsum
+	gnx[len(p)-1] = fnx - gnxsum
 
 	return gnx
 }