diff --git a/tests/wpt/mozilla/tests/mozilla/characterdata.html b/tests/wpt/mozilla/tests/mozilla/characterdata.html
index fe2dafa8675..f4f586e9aec 100644
--- a/tests/wpt/mozilla/tests/mozilla/characterdata.html
+++ b/tests/wpt/mozilla/tests/mozilla/characterdata.html
@@ -9,13 +9,7 @@
   <script>
   test(function() {
     var a = document.getElementsByTagName('p')[0].childNodes[0];
-    assert_equals(a.data, "This is the character data");
-    // append test utf8
-    a.appendData(", append more 資料，測試資料");
-    assert_equals(a.data, "This is the character data, append more 資料，測試資料");
-
-    // length test utf8
-    assert_equals(a.length, 47);
+    a.data = "This is the character data, append more 資料，測試資料";
 
     // insert test non-utf8
     a.insertData(26, " test");
diff --git a/tests/wpt/web-platform-tests/dom/nodes/CharacterData-appendData.html b/tests/wpt/web-platform-tests/dom/nodes/CharacterData-appendData.html
index 464a119a03d..d754218bfb1 100644
--- a/tests/wpt/web-platform-tests/dom/nodes/CharacterData-appendData.html
+++ b/tests/wpt/web-platform-tests/dom/nodes/CharacterData-appendData.html
@@ -24,6 +24,14 @@ function testNode(create, type) {
     assert_equals(node.data, "test")
   }, type + ".appendData('')")
 
+  test(function() {
+    var node = create()
+    assert_equals(node.data, "test")
+    node.appendData(", append more 資料，測試資料");
+    assert_equals(node.data, "test, append more 資料，測試資料");
+    assert_equals(node.length, 25);
+  }, type + ".appendData(non-ASCII)")
+
   test(function() {
     var node = create()
     assert_equals(node.data, "test")