diff --git a/js/url_search_params.ts b/js/url_search_params.ts
index 9f4621b7b3..13b272476b 100644
--- a/js/url_search_params.ts
+++ b/js/url_search_params.ts
@@ -19,6 +19,11 @@ export class URLSearchParams {
       return;
     }
 
+    if (init instanceof URLSearchParams) {
+      this.params = init.params;
+      return;
+    }
+
     // Overload: record<USVString, USVString>
     for (const key of Object.keys(init)) {
       this.append(key, init[key]);
diff --git a/js/url_search_params_test.ts b/js/url_search_params_test.ts
index 8da11382fa..0bce1166c5 100644
--- a/js/url_search_params_test.ts
+++ b/js/url_search_params_test.ts
@@ -22,6 +22,14 @@ test(function urlSearchParamsInitRecord(): void {
   assertEquals(searchParams.toString(), "a=54&b=true");
 });
 
+test(function urlSearchParamsInit(): void {
+  const params1 = new URLSearchParams("a=b");
+  assertEquals(params1.toString(), "a=b");
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const params2 = new URLSearchParams(params1 as any);
+  assertEquals(params2.toString(), "a=b");
+});
+
 test(function urlSearchParamsAppendSuccess(): void {
   const searchParams = new URLSearchParams();
   searchParams.append("a", "true");