diff --git a/Userland/Libraries/LibWeb/CSS/Selector.cpp b/Userland/Libraries/LibWeb/CSS/Selector.cpp
index 31e989109c..a95bc52311 100644
--- a/Userland/Libraries/LibWeb/CSS/Selector.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Selector.cpp
@@ -214,6 +214,7 @@ String Selector::SimpleSelector::serialize() const
         case Selector::SimpleSelector::PseudoClass::Type::Visited:
         case Selector::SimpleSelector::PseudoClass::Type::Hover:
         case Selector::SimpleSelector::PseudoClass::Type::Focus:
+        case Selector::SimpleSelector::PseudoClass::Type::FocusWithin:
         case Selector::SimpleSelector::PseudoClass::Type::FirstChild:
         case Selector::SimpleSelector::PseudoClass::Type::LastChild:
         case Selector::SimpleSelector::PseudoClass::Type::OnlyChild: