diff --git a/packages/router/src/router_module.ts b/packages/router/src/router_module.ts
index 13d6665e9ef..803fb2de477 100644
--- a/packages/router/src/router_module.ts
+++ b/packages/router/src/router_module.ts
@@ -181,7 +181,8 @@ export function provideForRootGuard(router: Router): any {
   if (NG_DEV_MODE && router) {
     throw new RuntimeError(
         RuntimeErrorCode.FOR_ROOT_CALLED_TWICE,
-        `RouterModule.forRoot() called twice. Lazy loaded modules should use RouterModule.forChild() instead.`);
+        `The Router was provided more than once. This can happen if 'forRoot' is used outside of the root injector.` +
+            ` Lazy loaded modules should use RouterModule.forChild() instead.`);
   }
   return 'guarded';
 }
diff --git a/packages/router/test/integration.spec.ts b/packages/router/test/integration.spec.ts
index b07b0b36975..12cafce2b79 100644
--- a/packages/router/test/integration.spec.ts
+++ b/packages/router/test/integration.spec.ts
@@ -5806,7 +5806,7 @@ describe('Integration', () => {
          let recordedError: any = null;
          router.navigateByUrl('/lazy/loaded')!.catch(err => recordedError = err);
          advance(fixture);
-         expect(recordedError.message).toContain(`RouterModule.forRoot() called twice.`);
+         expect(recordedError.message).toContain(`NG04007`);
        })));
 
     it('should combine routes from multiple modules into a single configuration',