1 files changed, 9 insertions, 2 deletions
diff --git a/components/script/dom/htmlcollection.rs b/components/script/dom/htmlcollection.rs
index aff4125a29f..7c3cad306c4 100644
--- a/components/script/dom/htmlcollection.rs
+++ b/components/script/dom/htmlcollection.rs
@@ -11,12 +11,14 @@ use dom::bindings::str::DOMString;
 use dom::bindings::trace::JSTraceable;
 use dom::bindings::xmlname::namespace_from_domstring;
 use dom::element::Element;
-use dom::node::Node;
+use dom::node::{Node, document_from_node};
 use dom::window::Window;
 use dom_struct::dom_struct;
 use html5ever::{LocalName, QualName};
+use selectors::attr::CaseSensitivity;
 use servo_atoms::Atom;
 use std::cell::Cell;
+use style::context::QuirksMode;
 use style::str::split_html_space_chars;
 
 pub trait CollectionFilter : JSTraceable {
@@ -199,7 +201,12 @@ impl HTMLCollection {
         }
         impl CollectionFilter for ClassNameFilter {
             fn filter(&self, elem: &Element, _root: &Node) -> bool {
-                self.classes.iter().all(|class| elem.has_class(class))
+                let case_sensitivity = match document_from_node(elem).quirks_mode() {
+                    QuirksMode::NoQuirks |
+                    QuirksMode::LimitedQuirks => CaseSensitivity::CaseSensitive,
+                    QuirksMode::Quirks => CaseSensitivity::AsciiCaseInsensitive,
+                };
+                self.classes.iter().all(|class| elem.has_class(class, case_sensitivity))
             }
         }
         let filter = ClassNameFilter {