diff --git a/Userland/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_h.cpp b/Userland/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_h.cpp
index 79d16e6406..e154ca45a4 100644
--- a/Userland/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_h.cpp
+++ b/Userland/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_h.cpp
@@ -53,6 +53,7 @@ namespace Web::CSS {
 
 enum class PropertyID {
     Invalid,
+    Custom,
 )~~~");
 
     json.value().as_object().for_each_member([&](auto& name, auto& value) {