diff --git a/src/x.js b/src/x.js
index b1cd053..894e748 100644
--- a/src/x.js
+++ b/src/x.js
@@ -20,8 +20,7 @@ export default function(x) {
     strengths = new Array(n);
     xz = new Array(n);
     for (i = 0; i < n; ++i) {
-      strengths[i] = +strength(nodes[i], i, nodes);
-      xz[i] = +x(nodes[i], i, nodes);
+      strengths[i] = isNaN(xz[i] = +x(nodes[i], i, nodes)) ? 0 : +strength(nodes[i], i, nodes);
     }
   }
 
diff --git a/src/y.js b/src/y.js
index 14a1c9b..bdf68e4 100644
--- a/src/y.js
+++ b/src/y.js
@@ -20,8 +20,7 @@ export default function(y) {
     strengths = new Array(n);
     yz = new Array(n);
     for (i = 0; i < n; ++i) {
-      strengths[i] = +strength(nodes[i], i, nodes);
-      yz[i] = +y(nodes[i], i, nodes);
+      strengths[i] = isNaN(yz[i] = +y(nodes[i], i, nodes)) ? 0 : +strength(nodes[i], i, nodes);
     }
   }