diff --git a/dom/base/CustomElementRegistry.cpp b/dom/base/CustomElementRegistry.cpp
index bd26e4ff32..82f15f6834 100644
--- a/dom/base/CustomElementRegistry.cpp
+++ b/dom/base/CustomElementRegistry.cpp
@@ -408,8 +408,7 @@ CustomElementRegistry::GetCustomPrototype(nsIAtom* aAtom,
 }
 
 void
-CustomElementRegistry::UpgradeCandidates(JSContext* aCx,
-                                         nsIAtom* aKey,
+CustomElementRegistry::UpgradeCandidates(nsIAtom* aKey,
                                          CustomElementDefinition* aDefinition,
                                          ErrorResult& aRv)
 {
@@ -719,7 +718,7 @@ CustomElementRegistry::Define(const nsAString& aName,
    * 13. 14. 15. Upgrade candidates
    */
   // TODO: Bug 1299363 - Implement custom element v1 upgrade algorithm
-  UpgradeCandidates(cx, nameAtom, definition, aRv);
+  UpgradeCandidates(nameAtom, definition, aRv);
 
   /**
    * 16. If this CustomElementRegistry's when-defined promise map contains an
diff --git a/dom/base/CustomElementRegistry.h b/dom/base/CustomElementRegistry.h
index 84a7fe3acb..db208bf713 100644
--- a/dom/base/CustomElementRegistry.h
+++ b/dom/base/CustomElementRegistry.h
@@ -346,8 +346,7 @@ private:
   void RegisterUnresolvedElement(Element* aElement,
                                  nsIAtom* aTypeName = nullptr);
 
-  void UpgradeCandidates(JSContext* aCx,
-                         nsIAtom* aKey,
+  void UpgradeCandidates(nsIAtom* aKey,
                          CustomElementDefinition* aDefinition,
                          ErrorResult& aRv);