diff --git a/Libraries/LibWeb/DOM/Element.cpp b/Libraries/LibWeb/DOM/Element.cpp
index 6cccaeaf3bd..292e91b2cf6 100644
--- a/Libraries/LibWeb/DOM/Element.cpp
+++ b/Libraries/LibWeb/DOM/Element.cpp
@@ -90,7 +90,6 @@ Element::Element(Document& document, DOM::QualifiedName qualified_name)
     : ParentNode(document, NodeType::ELEMENT_NODE)
     , m_qualified_name(move(qualified_name))
 {
-    make_html_uppercased_qualified_name();
 }
 
 Element::~Element() = default;
@@ -952,13 +951,12 @@ void Element::set_inline_style(GC::Ptr<CSS::CSSStyleProperties> style)
 }
 
 // https://dom.spec.whatwg.org/#element-html-uppercased-qualified-name
-void Element::make_html_uppercased_qualified_name()
+FlyString Element::make_html_uppercased_qualified_name() const
 {
     // This is allowed by the spec: "User agents could optimize qualified name and HTML-uppercased qualified name by storing them in internal slots."
     if (namespace_uri() == Namespace::HTML && document().document_type() == Document::Type::HTML)
-        m_html_uppercased_qualified_name = qualified_name().to_ascii_uppercase();
-    else
-        m_html_uppercased_qualified_name = qualified_name();
+        return qualified_name().to_ascii_uppercase();
+    return qualified_name();
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#queue-an-element-task
@@ -3853,4 +3851,11 @@ GC::Ptr<NamedNodeMap const> Element::attributes() const
     return const_cast<Element&>(*this).attributes();
 }
 
+FlyString const& Element::html_uppercased_qualified_name() const
+{
+    if (!m_html_uppercased_qualified_name.has_value())
+        m_html_uppercased_qualified_name = make_html_uppercased_qualified_name();
+    return m_html_uppercased_qualified_name.value();
+}
+
 }
diff --git a/Libraries/LibWeb/DOM/Element.h b/Libraries/LibWeb/DOM/Element.h
index 5bf5e5a7ac8..715599de439 100644
--- a/Libraries/LibWeb/DOM/Element.h
+++ b/Libraries/LibWeb/DOM/Element.h
@@ -110,7 +110,7 @@ public:
     virtual ~Element() override;
 
     FlyString const& qualified_name() const { return m_qualified_name.as_string(); }
-    FlyString const& html_uppercased_qualified_name() const { return m_html_uppercased_qualified_name; }
+    FlyString const& html_uppercased_qualified_name() const;
 
     virtual FlyString node_name() const final { return html_uppercased_qualified_name(); }
     FlyString const& local_name() const { return m_qualified_name.local_name(); }
@@ -497,7 +497,7 @@ protected:
     CustomElementState custom_element_state() const { return m_custom_element_state; }
 
 private:
-    void make_html_uppercased_qualified_name();
+    FlyString make_html_uppercased_qualified_name() const;
 
     void invalidate_style_after_attribute_change(FlyString const& attribute_name, Optional<String> const& old_value, Optional<String> const& new_value);
 
@@ -511,7 +511,7 @@ private:
     bool is_auto_directionality_form_associated_element() const;
 
     QualifiedName m_qualified_name;
-    FlyString m_html_uppercased_qualified_name;
+    mutable Optional<FlyString> m_html_uppercased_qualified_name;
 
     GC::Ptr<NamedNodeMap> m_attributes;
     GC::Ptr<CSS::CSSStyleProperties> m_inline_style;