diff --git a/src/path/bounds.js b/src/path/bounds.js
index 0c83258..f079562 100644
--- a/src/path/bounds.js
+++ b/src/path/bounds.js
@@ -19,6 +19,8 @@ var boundsStream = {
 };
 
 function boundsPoint(x, y) {
+  x = +x;
+  y = +y;
   if (x < x0) x0 = x;
   if (x > x1) x1 = x;
   if (y < y0) y0 = y;