diff --git a/src/HttpClient.ts b/src/HttpClient.ts
index 72d87368..3f1efd3f 100644
--- a/src/HttpClient.ts
+++ b/src/HttpClient.ts
@@ -201,7 +201,8 @@ export class HttpClient extends EventEmitter {
         // url maybe url.parse(url) object in urllib2
         requestUrl = new URL(urlFormat(url));
       } else {
-        requestUrl = url;
+        // or even if not, we clone to avoid mutating it
+        requestUrl = new URL(url.toString());
       }
     }
 
diff --git a/test/options.data.test.ts b/test/options.data.test.ts
index 71b13e6d..6e7e65ef 100644
--- a/test/options.data.test.ts
+++ b/test/options.data.test.ts
@@ -43,6 +43,15 @@ describe('options.data.test.ts', () => {
     assert.equal(url.searchParams.get('data'), '哈哈');
   });
 
+  it('should not mutate a passed URL object when setting query string', async () => {
+    const url = new URL(_url);
+    assert.equal(url.searchParams.get('param1'), null);
+    await urllib.request(url, {
+      data: { param1: 'val1' },
+    });
+    assert.equal(url.searchParams.get('param1'), null);
+  });
+
   it('should GET with data work on nestedQuerystring=true', async () => {
     const response = await urllib.request(_url, {
       method: 'GET',