diff --git a/modules/@angular/common/src/directives/ng_class.ts b/modules/@angular/common/src/directives/ng_class.ts
index 4a318355bd..9b8ad0129e 100644
--- a/modules/@angular/common/src/directives/ng_class.ts
+++ b/modules/@angular/common/src/directives/ng_class.ts
@@ -9,7 +9,7 @@
 import {CollectionChangeRecord, Directive, DoCheck, ElementRef, Input, IterableDiffer, IterableDiffers, KeyValueChangeRecord, KeyValueDiffer, KeyValueDiffers, Renderer} from '@angular/core';
 
 import {isListLikeIterable} from '../facade/collection';
-import {isPresent} from '../facade/lang';
+import {isPresent, stringify} from '../facade/lang';
 
 /**
  * @ngModule CommonModule
@@ -108,8 +108,14 @@ export class NgClass implements DoCheck {
   }
 
   private _applyIterableChanges(changes: any): void {
-    changes.forEachAddedItem(
-        (record: CollectionChangeRecord) => this._toggleClass(record.item, true));
+    changes.forEachAddedItem((record: CollectionChangeRecord) => {
+      if (typeof record.item === 'string') {
+        this._toggleClass(record.item, true);
+      } else {
+        throw new Error(
+            `NgClass can only toggle CSS classes expressed as strings, got ${stringify(record.item)}`);
+      }
+    });
 
     changes.forEachRemovedItem(
         (record: CollectionChangeRecord) => this._toggleClass(record.item, false));
diff --git a/modules/@angular/common/test/directives/ng_class_spec.ts b/modules/@angular/common/test/directives/ng_class_spec.ts
index 1536939055..355c51430e 100644
--- a/modules/@angular/common/test/directives/ng_class_spec.ts
+++ b/modules/@angular/common/test/directives/ng_class_spec.ts
@@ -8,7 +8,6 @@
 
 import {Component} from '@angular/core';
 import {ComponentFixture, TestBed, async} from '@angular/core/testing';
-import {beforeEach, describe, expect, it} from '@angular/core/testing/testing_internal';
 
 export function main() {
   describe('binding to CSS class list', () => {
@@ -187,6 +186,13 @@ export function main() {
            getComponent().arrExpr = ['foo bar   baz foobar'];
            detectChangesAndExpectClassName('foo bar baz foobar');
          }));
+
+      it('should throw with descriptive error message when CSS class is not a string', () => {
+        fixture = createTestComponent(`<div [ngClass]="['foo', {}]"></div>`);
+        expect(() => fixture.detectChanges())
+            .toThrowError(
+                /NgClass can only toggle CSS classes expressed as strings, got \[object Object\]/);
+      });
     });
 
     describe('expressions evaluating to sets', () => {
@@ -348,4 +354,4 @@ class TestComponent {
 function createTestComponent(template: string): ComponentFixture<TestComponent> {
   return TestBed.overrideComponent(TestComponent, {set: {template: template}})
       .createComponent(TestComponent);
-}
\ No newline at end of file
+}