diff --git a/types/ember/index.d.ts b/types/ember/index.d.ts
index adef4e70c2..5e77e49233 100755
--- a/types/ember/index.d.ts
+++ b/types/ember/index.d.ts
@@ -300,7 +300,7 @@ declare module 'ember' {
             /**
              * Given a fullName return a corresponding instance.
              */
-            lookup(fullName: string, options: {}): any;
+            lookup(fullName: string, options?: {}): any;
         }
         const _ContainerProxyMixin: Mixin<_ContainerProxyMixin>;