diff --git a/components/script/dom/attr.rs b/components/script/dom/attr.rs
index 2b8213718191..a848ca85e0c8 100644
--- a/components/script/dom/attr.rs
+++ b/components/script/dom/attr.rs
@@ -38,8 +38,12 @@ pub enum AttrValue {
 
 impl AttrValue {
     pub fn from_serialized_tokenlist(tokens: DOMString) -> AttrValue {
-        let atoms = split_html_space_chars(tokens.as_slice())
-            .map(|token| Atom::from_slice(token)).collect();
+        let mut atoms: Vec<Atom> = vec!();
+        for token in split_html_space_chars(tokens.as_slice()).map(|slice| Atom::from_slice(slice)) {
+            if !atoms.iter().any(|atom| *atom == token) {
+                atoms.push(token);
+            }
+        }
         AttrValue::TokenList(tokens, atoms)
     }
 
diff --git a/tests/wpt/metadata/dom/nodes/Element-classlist.html.ini b/tests/wpt/metadata/dom/nodes/Element-classlist.html.ini
index c072735d5026..3ec7b9070e15 100644
--- a/tests/wpt/metadata/dom/nodes/Element-classlist.html.ini
+++ b/tests/wpt/metadata/dom/nodes/Element-classlist.html.ini
@@ -3,9 +3,6 @@
   [CSS .foo selectors must not match elements without any class]
     expected: FAIL
 
-  [classList must be correct for an element that has classes]
-    expected: FAIL
-
   [empty classList should return the empty string since the ordered set parser skip the whitespaces]
     expected: FAIL
 
@@ -63,9 +60,6 @@
   [classList.remove must not break case-sensitive CSS selector matching]
     expected: FAIL
 
-  [classList.remove must remove duplicated tokens]
-    expected: FAIL
-
   [classList.remove must collapse whitespace around removed tokens]
     expected: FAIL