diff --git a/Userland/Libraries/LibWeb/CSS/CSSRule.cpp b/Userland/Libraries/LibWeb/CSS/CSSRule.cpp
index 79872b5b700..653b8a0a1c1 100644
--- a/Userland/Libraries/LibWeb/CSS/CSSRule.cpp
+++ b/Userland/Libraries/LibWeb/CSS/CSSRule.cpp
@@ -41,11 +41,18 @@ void CSSRule::set_css_text(StringView)
 void CSSRule::set_parent_rule(CSSRule* parent_rule)
 {
     m_parent_rule = parent_rule;
+    clear_caches();
 }
 
 void CSSRule::set_parent_style_sheet(CSSStyleSheet* parent_style_sheet)
 {
     m_parent_style_sheet = parent_style_sheet;
+    clear_caches();
+}
+
+void CSSRule::clear_caches()
+{
+    m_cached_layer_name.clear();
 }
 
 FlyString const& CSSRule::parent_layer_internal_qualified_name_slow_case() const
diff --git a/Userland/Libraries/LibWeb/CSS/CSSRule.h b/Userland/Libraries/LibWeb/CSS/CSSRule.h
index 28929d41f46..c84527f35a2 100644
--- a/Userland/Libraries/LibWeb/CSS/CSSRule.h
+++ b/Userland/Libraries/LibWeb/CSS/CSSRule.h
@@ -60,6 +60,8 @@ protected:
 
     virtual void visit_edges(Cell::Visitor&) override;
 
+    virtual void clear_caches();
+
     [[nodiscard]] FlyString const& parent_layer_internal_qualified_name() const
     {
         if (!m_cached_layer_name.has_value())