diff --git a/components/script/dom/cssrule.rs b/components/script/dom/cssrule.rs
index a541ee411c7..5945123ac51 100644
--- a/components/script/dom/cssrule.rs
+++ b/components/script/dom/cssrule.rs
@@ -105,6 +105,7 @@ impl CSSRule {
             },
             StyleCssRule::Page(_) => unreachable!(),
             StyleCssRule::Document(_) => unimplemented!(), // TODO
+            StyleCssRule::Layer(_) => unimplemented!(),    // TODO
         }
     }