diff --git a/test/src/basic_sum_AB.js b/test/src/basic_sum_AB.js
index 363bdf2b..990ec71a 100644
--- a/test/src/basic_sum_AB.js
+++ b/test/src/basic_sum_AB.js
@@ -70,7 +70,7 @@ float _coordToIndex_(vec2 coord) {
 
 void main(float* a, float* b) {
     vec2 _vecId_ = get_global_id();
-	float _id_ = _vecId_.x + _vecId_.y * _W_;
+	float _id_ = _coordToIndex_(_vecId_);
 	
 	vec3 _thread_ = _indexTo3D_(_id_);