diff --git a/packages/@ember/routing/route.ts b/packages/@ember/routing/route.ts
index 9fe668a6e5f..94e3d15ea58 100644
--- a/packages/@ember/routing/route.ts
+++ b/packages/@ember/routing/route.ts
@@ -335,7 +335,7 @@ class Route<Model = unknown> extends EmberObject.extend(ActionHandler, Evented)
     @since 1.0.0
     @public
   */
-  serialize(model: Model | undefined, params: string[]): { [key: string]: unknown } | undefined {
+  serialize(model: Model, params: string[]): { [key: string]: unknown } | undefined {
     if (params.length < 1 || !model) {
       return;
     }
diff --git a/type-tests/@ember/routing-test/route.ts b/type-tests/@ember/routing-test/route.ts
index d46c61cb460..afdf1e1831b 100755
--- a/type-tests/@ember/routing-test/route.ts
+++ b/type-tests/@ember/routing-test/route.ts
@@ -35,6 +35,27 @@ class ModelTest extends Route {
   }
 }
 
+class Model {
+  baseClass = true;
+}
+
+class Child extends Model {
+  baseClass = false;
+  extraStuff = true;
+}
+
+class FooRoute<T extends Model> extends Route<T> {
+  serialize(object: T): any {
+    return null;
+  }
+}
+
+class FooChildRoute extends FooRoute<Child> {
+  serialize(object: Child) {
+    return object.extraStuff;
+  }
+}
+
 class QPsTest extends Route {
   queryParams = {
     memberQp: { refreshModel: true },