diff --git a/modules/@angular/compiler-cli/src/ngtools_impl.ts b/modules/@angular/compiler-cli/src/ngtools_impl.ts
index 9b81320fd25e4f..5cebb5902f2547 100644
--- a/modules/@angular/compiler-cli/src/ngtools_impl.ts
+++ b/modules/@angular/compiler-cli/src/ngtools_impl.ts
@@ -192,7 +192,7 @@ function _collectRoutes(
  */
 function _collectLoadChildren(routes: Route[]): string[] {
   return routes.reduce((m, r) => {
-    if (r.loadChildren) {
+    if (r.loadChildren && typeof r.loadChildren === 'string') {
       return m.concat(r.loadChildren);
     } else if (Array.isArray(r)) {
       return m.concat(_collectLoadChildren(r));