diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index 87804d373fd..0ca9c3c3f90 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -95,6 +95,7 @@ pub struct Element {
     namespace: Namespace,
     prefix: Option<DOMString>,
     attrs: DOMRefCell<Vec<JS<Attr>>>,
+    id_attribute: DOMRefCell<Option<Atom>>,
     style_attribute: DOMRefCell<Option<PropertyDeclarationBlock>>,
     attr_list: MutNullableHeap<JS<NamedNodeMap>>,
     class_list: MutNullableHeap<JS<DOMTokenList>>,
@@ -149,6 +150,7 @@ impl Element {
             attrs: DOMRefCell::new(vec!()),
             attr_list: Default::default(),
             class_list: Default::default(),
+            id_attribute: DOMRefCell::new(None),
             style_attribute: DOMRefCell::new(None),
         }
     }
@@ -1466,6 +1468,15 @@ impl VirtualMethods for Element {
                 NodeDamage::NodeStyleDamaged
             },
             &atom!(id) => {
+                *self.id_attribute.borrow_mut() =
+                    mutation.new_value(attr).and_then(|value| {
+                        let value = value.as_atom();
+                        if value != &atom!("") {
+                            Some(value.clone())
+                        } else {
+                            None
+                        }
+                    });
                 if node.is_in_doc() {
                     let value = attr.value().as_atom().clone();
                     match mutation {
@@ -1512,13 +1523,9 @@ impl VirtualMethods for Element {
 
         if !tree_in_doc { return; }
 
-        if let Some(ref attr) = self.get_attribute(&ns!(""), &atom!("id")) {
-            let value = attr.value();
-            if !value.is_empty() {
-                let doc = document_from_node(self);
-                let value = Atom::from_slice(&value);
-                doc.register_named_element(self, value.to_owned());
-            }
+        if let Some(ref value) = *self.id_attribute.borrow() {
+            let doc = document_from_node(self);
+            doc.register_named_element(self, value.clone());
         }
     }
 
@@ -1529,13 +1536,9 @@ impl VirtualMethods for Element {
 
         if !tree_in_doc { return; }
 
-        if let Some(ref attr) = self.get_attribute(&ns!(""), &atom!("id")) {
-            let value = attr.value();
-            if !value.is_empty() {
-                let doc = document_from_node(self);
-                let value = Atom::from_slice(&value);
-                doc.unregister_named_element(self, value.to_owned());
-            }
+        if let Some(ref value) = *self.id_attribute.borrow() {
+            let doc = document_from_node(self);
+            doc.unregister_named_element(self, value.clone());
         }
     }
 }
@@ -1621,12 +1624,7 @@ impl<'a> ::selectors::Element for Root<Element> {
         node.get_focus_state()
     }
     fn get_id(&self) -> Option<Atom> {
-        self.get_attribute(&ns!(""), &atom!("id")).map(|attr| {
-            match *attr.r().value() {
-                AttrValue::Atom(ref val) => val.clone(),
-                _ => panic!("`id` attribute should be AttrValue::Atom"),
-            }
-        })
+        self.id_attribute.borrow().clone()
     }
     fn get_disabled_state(&self) -> bool {
         let node = NodeCast::from_ref(&**self);
diff --git a/tests/unit/script/size_of.rs b/tests/unit/script/size_of.rs
index 1b34e462470..7eec6699f19 100644
--- a/tests/unit/script/size_of.rs
+++ b/tests/unit/script/size_of.rs
@@ -40,9 +40,9 @@ macro_rules! sizeof_checker (
 // Update the sizes here
 sizeof_checker!(size_event_target, EventTarget, 40);
 sizeof_checker!(size_node, Node, 168);
-sizeof_checker!(size_element, Element, 280);
-sizeof_checker!(size_htmlelement, HTMLElement, 296);
-sizeof_checker!(size_div, HTMLDivElement, 296);
-sizeof_checker!(size_span, HTMLSpanElement, 296);
+sizeof_checker!(size_element, Element, 304);
+sizeof_checker!(size_htmlelement, HTMLElement, 320);
+sizeof_checker!(size_div, HTMLDivElement, 320);
+sizeof_checker!(size_span, HTMLSpanElement, 320);
 sizeof_checker!(size_text, Text, 200);
 sizeof_checker!(size_characterdata, CharacterData, 200);