diff --git a/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp b/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
index 43794e2f6b..d31b7ad564 100644
--- a/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
+++ b/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
@@ -341,6 +341,9 @@ static inline bool matches(CSS::Selector::SimpleSelector const& component, DOM::
     case CSS::Selector::SimpleSelector::Type::Class:
         return element.has_class(component.name());
     case CSS::Selector::SimpleSelector::Type::TagName:
+        // See https://html.spec.whatwg.org/multipage/semantics-other.html#case-sensitivity-of-selectors
+        if (is<HTML::HTMLElement>(element) && element.document().document_type() != DOM::Document::Type::XML)
+            return component.name().equals_ignoring_case(element.local_name());
         return component.name() == element.local_name();
     case CSS::Selector::SimpleSelector::Type::Attribute:
         return matches_attribute(component.attribute(), element);