diff --git a/lib/internal/url.js b/lib/internal/url.js
index 9c18aab07ff19d..c2d2971e168a37 100644
--- a/lib/internal/url.js
+++ b/lib/internal/url.js
@@ -767,7 +767,11 @@ ObjectDefineProperties(URLSearchParams.prototype, {
  * @returns {self is URL}
  */
 function isURL(self) {
-  return Boolean(self?.href && self.protocol && self.auth === undefined && self.path === undefined);
+  return Boolean(typeof self === 'object' &&
+                 self?.href &&
+                 self.protocol &&
+                 self.auth === undefined &&
+                 self.path === undefined);
 }
 
 /**