diff --git a/components/script/dom/extendableevent.rs b/components/script/dom/extendableevent.rs
index 76756b40c71..ffb6c3baad2 100644
--- a/components/script/dom/extendableevent.rs
+++ b/components/script/dom/extendableevent.rs
@@ -51,7 +51,7 @@ impl ExtendableEvent {
     }
 
     // https://w3c.github.io/ServiceWorker/#wait-until-method
-    pub fn WaitUntil(&self, _cx: *mut JSContext, val: HandleValue) -> ErrorResult {
+    pub fn WaitUntil(&self, _cx: *mut JSContext, _val: HandleValue) -> ErrorResult {
         // Step 1
         if !self.extensions_allowed {
             return Err(Error::InvalidState);