diff --git a/lib/jiti-native.mjs b/lib/jiti-native.mjs
index 6113be24..f8e16468 100644
--- a/lib/jiti-native.mjs
+++ b/lib/jiti-native.mjs
@@ -111,7 +111,7 @@ function normalizeParentURL(input) {
   if (!input) {
     return "file:///";
   }
-  if (input instanceof URL || input.startsWith("file://")) {
+  if (typeof filename !== "string" || input.startsWith("file://")) {
     return input;
   }
   if (input.endsWith("/")) {
diff --git a/src/utils.ts b/src/utils.ts
index ca398a16..6acc8f21 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -8,7 +8,7 @@ import type { Context } from "./types";
 import { gray, green, blue, yellow, cyan, red } from "yoctocolors";
 
 export function isDir(filename: string | URL): boolean {
-  if (filename instanceof URL || filename.startsWith("file://")) {
+  if (typeof filename !== "string" || filename.startsWith("file://")) {
     return false;
   }
   try {