diff --git a/src/api/test-page-url.ts b/src/api/test-page-url.ts
index 6370134a5a8..5c9bb0e1365 100644
--- a/src/api/test-page-url.ts
+++ b/src/api/test-page-url.ts
@@ -51,8 +51,18 @@ export function getUrl (url: string, base?: URL): string {
 }
 
 export function prepareBaseUrl (url: string): URL {
-    url = join(url, '/');
-    return isAbsolute(url) ? pathToFileURL(url) : new URL(url);
+    // If it's a web URL (http/https), use it directly
+    if (/^https?:\/\//i.test(url)) {
+        return new URL(url.endsWith('/') ? url : url + '/');
+    }
+
+    // Handle file URLs explicitly
+    if (/^file:\/\//i.test(url)) {
+        return new URL(url);
+    }
+
+    // Otherwise, treat it as filesystem path
+    return pathToFileURL(isAbsolute(url) ? url : join(process.cwd(), url));
 }
 
 export function assertPageUrl (url: string, callsiteName: string): void {