diff --git a/src/selector.js b/src/selector.js
index 0ca8cf5..d039a2d 100644
--- a/src/selector.js
+++ b/src/selector.js
@@ -73,9 +73,9 @@ export default function(random) {
 
     match({ count, grid, x, y }) {
       return expr => {
-        return !!calc(expr, {
+        return !!calc('(' + expr + ')', {
           x, y,
-          X: grid.x, Y: grid.Y,
+          X: grid.x, Y: grid.y,
           i: count,
         });
       }