diff --git a/src/observe.js b/src/observe.js
index 82afaf4..6cc6819 100644
--- a/src/observe.js
+++ b/src/observe.js
@@ -139,6 +139,8 @@
     }
   }
 
+  Path.isValid = isPathValid;
+
   Path.prototype = createObject({
     __proto__: [],