diff --git a/Libraries/LibWeb/CSS/StyleComputer.cpp b/Libraries/LibWeb/CSS/StyleComputer.cpp
index eca04ed3e58..b74e5e212c4 100644
--- a/Libraries/LibWeb/CSS/StyleComputer.cpp
+++ b/Libraries/LibWeb/CSS/StyleComputer.cpp
@@ -2656,9 +2656,6 @@ void StyleComputer::collect_selector_insights(Selector const& selector, Selector
                 if (simple_selector.pseudo_class().type == PseudoClass::Has) {
                     insights.has_has_selectors = true;
                 }
-                if (simple_selector.pseudo_class().type == PseudoClass::Defined) {
-                    insights.has_defined_selectors = true;
-                }
                 for (auto const& argument_selector : simple_selector.pseudo_class().argument_selector_list) {
                     collect_selector_insights(*argument_selector, insights);
                 }
@@ -3175,13 +3172,4 @@ bool StyleComputer::may_have_has_selectors() const
     return m_selector_insights->has_has_selectors;
 }
 
-bool StyleComputer::may_have_defined_selectors() const
-{
-    if (!has_valid_rule_cache())
-        return true;
-
-    build_rule_cache_if_needed();
-    return m_selector_insights->has_defined_selectors;
-}
-
 }
diff --git a/Libraries/LibWeb/CSS/StyleComputer.h b/Libraries/LibWeb/CSS/StyleComputer.h
index 07631eb4b68..3d26c17070c 100644
--- a/Libraries/LibWeb/CSS/StyleComputer.h
+++ b/Libraries/LibWeb/CSS/StyleComputer.h
@@ -177,7 +177,6 @@ public:
     void collect_animation_into(DOM::Element&, Optional<CSS::Selector::PseudoElement::Type>, GC::Ref<Animations::KeyframeEffect> animation, ComputedProperties&, AnimationRefresh = AnimationRefresh::No) const;
 
     [[nodiscard]] bool may_have_has_selectors() const;
-    [[nodiscard]] bool may_have_defined_selectors() const;
 
     size_t number_of_css_font_faces_with_loading_in_progress() const;
 
@@ -257,7 +256,6 @@ private:
 
     struct SelectorInsights {
         bool has_has_selectors { false };
-        bool has_defined_selectors { false };
     };
 
     struct RuleCache {
diff --git a/Libraries/LibWeb/CSS/StyleInvalidationData.cpp b/Libraries/LibWeb/CSS/StyleInvalidationData.cpp
index 8acc5a5ec8a..af281ffb15c 100644
--- a/Libraries/LibWeb/CSS/StyleInvalidationData.cpp
+++ b/Libraries/LibWeb/CSS/StyleInvalidationData.cpp
@@ -69,6 +69,7 @@ static void collect_properties_used_in_has(Selector::SimpleSelector const& selec
         switch (pseudo_class.type) {
         case PseudoClass::Enabled:
         case PseudoClass::Disabled:
+        case PseudoClass::Defined:
         case PseudoClass::PlaceholderShown:
         case PseudoClass::Checked:
             if (in_has)
@@ -122,6 +123,7 @@ static void build_invalidation_sets_for_simple_selector(Selector::SimpleSelector
         auto const& pseudo_class = selector.pseudo_class();
         switch (pseudo_class.type) {
         case PseudoClass::Enabled:
+        case PseudoClass::Defined:
         case PseudoClass::Disabled:
         case PseudoClass::PlaceholderShown:
         case PseudoClass::Checked:
diff --git a/Libraries/LibWeb/DOM/Element.cpp b/Libraries/LibWeb/DOM/Element.cpp
index abe92b2e2f4..22b1ee4c5bd 100644
--- a/Libraries/LibWeb/DOM/Element.cpp
+++ b/Libraries/LibWeb/DOM/Element.cpp
@@ -1183,6 +1183,9 @@ bool Element::includes_properties_from_invalidation_set(CSS::InvalidationSet con
             case CSS::PseudoClass::Disabled: {
                 return is_actually_disabled();
             }
+            case CSS::PseudoClass::Defined: {
+                return is_defined();
+            }
             case CSS::PseudoClass::Checked: {
                 // FIXME: This could be narrowed down to return true only if element is actually checked.
                 return is<HTML::HTMLInputElement>(*this) || is<HTML::HTMLOptionElement>(*this);
@@ -2366,8 +2369,9 @@ void Element::set_custom_element_state(CustomElementState state)
         return;
     m_custom_element_state = state;
 
-    if (document().style_computer().may_have_defined_selectors())
-        invalidate_style(StyleInvalidationReason::CustomElementStateChange);
+    Vector<CSS::InvalidationSet::Property, 1> changed_properties;
+    changed_properties.append({ .type = CSS::InvalidationSet::Property::Type::PseudoClass, .value = CSS::PseudoClass::Defined });
+    invalidate_style(StyleInvalidationReason::CustomElementStateChange, changed_properties, {});
 }
 
 // https://html.spec.whatwg.org/multipage/dom.html#html-element-constructors