diff --git a/packages/ember-runtime/lib/system/array_proxy.js b/packages/ember-runtime/lib/system/array_proxy.js
index ca266436a6c..e1bc27ef5d7 100644
--- a/packages/ember-runtime/lib/system/array_proxy.js
+++ b/packages/ember-runtime/lib/system/array_proxy.js
@@ -4,11 +4,13 @@
 
 import {
   get,
+  set,
   objectAt,
   alias,
   PROPERTY_DID_CHANGE,
   addArrayObserver,
   removeArrayObserver,
+  replace,
 } from 'ember-metal';
 import EmberObject from './object';
 import { isArray, MutableArray } from '../mixins/array';
@@ -193,6 +195,26 @@ export default class ArrayProxy extends EmberObject {
     return this._length;
   }
 
+  set length(value) {
+    let length = this.length;
+    let removedCount = length - value;
+
+    if (removedCount === 0) {
+      return;
+    } else if (removedCount < 0) {
+      throw new Error(`Cannot set array proxy length to a larger value (in ${this})`);
+    }
+
+    let content = get(this, 'content');
+    if (content) {
+      replace(content, value, removedCount);
+
+      this._lengthDirty = true;
+      this._objectsDirtyIndex = 0;
+      this._objects = null;
+    }
+  }
+
   [PROPERTY_DID_CHANGE](key) {
     if (key === 'arrangedContent') {
       let oldLength = this._objects === null ? 0 : this._objects.length;
diff --git a/packages/ember-runtime/tests/system/array_proxy/content_change_test.js b/packages/ember-runtime/tests/system/array_proxy/content_change_test.js
index e9c41511fe2..1c60e309d6c 100644
--- a/packages/ember-runtime/tests/system/array_proxy/content_change_test.js
+++ b/packages/ember-runtime/tests/system/array_proxy/content_change_test.js
@@ -1,6 +1,5 @@
 import { run } from '@ember/runloop';
-import { get, set, changeProperties } from 'ember-metal';
-import { not } from '@ember/object/computed';
+import { set, changeProperties } from 'ember-metal';
 import ArrayProxy from '../../../lib/system/array_proxy';
 import { A as emberA } from '../../../lib/mixins/array';
 import { moduleFor, AbstractTestCase } from 'internal-test-helpers';
@@ -8,38 +7,6 @@ import { moduleFor, AbstractTestCase } from 'internal-test-helpers';
 moduleFor(
   'ArrayProxy - content change',
   class extends AbstractTestCase {
-    ['@test should update length for null content'](assert) {
-      let proxy = ArrayProxy.create({
-        content: emberA([1, 2, 3]),
-      });
-
-      assert.equal(proxy.get('length'), 3, 'precond - length is 3');
-
-      proxy.set('content', null);
-
-      assert.equal(proxy.get('length'), 0, 'length updates');
-    }
-
-    ['@test should update length for null content when there is a computed property watching length'](
-      assert
-    ) {
-      let proxy = ArrayProxy.extend({
-        isEmpty: not('length'),
-      }).create({
-        content: emberA([1, 2, 3]),
-      });
-
-      assert.equal(proxy.get('length'), 3, 'precond - length is 3');
-
-      // Consume computed property that depends on length
-      proxy.get('isEmpty');
-
-      // update content
-      proxy.set('content', null);
-
-      assert.equal(proxy.get('length'), 0, 'length updates');
-    }
-
     ["@test The ArrayProxy doesn't explode when assigned a destroyed object"](assert) {
       let proxy1 = ArrayProxy.create();
       let proxy2 = ArrayProxy.create();
@@ -92,32 +59,6 @@ moduleFor(
       assert.deepEqual(indexes, [2, 3, 4]);
     }
 
-    ['@test getting length does not recompute the object cache'](assert) {
-      let indexes = [];
-
-      let proxy = ArrayProxy.extend({
-        objectAtContent(index) {
-          indexes.push(index);
-          return this.content[index];
-        },
-      }).create({
-        content: emberA([1, 2, 3, 4, 5]),
-      });
-
-      assert.equal(get(proxy, 'length'), 5);
-      assert.deepEqual(indexes, []);
-
-      indexes.length = 0;
-      proxy.set('content', emberA([6, 7, 8]));
-      assert.equal(get(proxy, 'length'), 3);
-      assert.deepEqual(indexes, []);
-
-      indexes.length = 0;
-      proxy.content.replace(1, 0, [1, 2, 3]);
-      assert.equal(get(proxy, 'length'), 6);
-      assert.deepEqual(indexes, []);
-    }
-
     ['@test negative indexes are handled correctly'](assert) {
       let indexes = [];
 
diff --git a/packages/ember-runtime/tests/system/array_proxy/length_test.js b/packages/ember-runtime/tests/system/array_proxy/length_test.js
index cf3fe267c5e..3be327341b0 100644
--- a/packages/ember-runtime/tests/system/array_proxy/length_test.js
+++ b/packages/ember-runtime/tests/system/array_proxy/length_test.js
@@ -1,13 +1,138 @@
 import ArrayProxy from '../../../lib/system/array_proxy';
 import EmberObject from '../../../lib/system/object';
 import { observer } from 'ember-metal';
-import { oneWay as reads } from '@ember/object/computed';
+import { oneWay as reads, not } from '@ember/object/computed';
 import { A as a } from '../../../lib/mixins/array';
 import { moduleFor, AbstractTestCase } from 'internal-test-helpers';
+import { set, get } from 'ember-metal';
 
 moduleFor(
   'Ember.ArrayProxy - content change (length)',
   class extends AbstractTestCase {
+    ['@test should update length for null content'](assert) {
+      let proxy = ArrayProxy.create({
+        content: a([1, 2, 3]),
+      });
+
+      assert.equal(proxy.get('length'), 3, 'precond - length is 3');
+
+      proxy.set('content', null);
+
+      assert.equal(proxy.get('length'), 0, 'length updates');
+    }
+
+    ['@test should update length for null content when there is a computed property watching length'](
+      assert
+    ) {
+      let proxy = ArrayProxy.extend({
+        isEmpty: not('length'),
+      }).create({
+        content: a([1, 2, 3]),
+      });
+
+      assert.equal(proxy.get('length'), 3, 'precond - length is 3');
+
+      // Consume computed property that depends on length
+      proxy.get('isEmpty');
+
+      // update content
+      proxy.set('content', null);
+
+      assert.equal(proxy.get('length'), 0, 'length updates');
+    }
+
+    ['@test getting length does not recompute the object cache'](assert) {
+      let indexes = [];
+
+      let proxy = ArrayProxy.extend({
+        objectAtContent(index) {
+          indexes.push(index);
+          return this.content[index];
+        },
+      }).create({
+        content: a([1, 2, 3, 4, 5]),
+      });
+
+      assert.equal(get(proxy, 'length'), 5);
+      assert.deepEqual(indexes, []);
+
+      indexes.length = 0;
+      proxy.set('content', a([6, 7, 8]));
+      assert.equal(get(proxy, 'length'), 3);
+      assert.deepEqual(indexes, []);
+
+      indexes.length = 0;
+      proxy.content.replace(1, 0, [1, 2, 3]);
+      assert.equal(get(proxy, 'length'), 6);
+      assert.deepEqual(indexes, []);
+    }
+
+    '@test accessing length after content set to null'(assert) {
+      let obj = ArrayProxy.create({ content: ['foo', 'bar'] });
+
+      assert.equal(obj.length, 2, 'precond');
+
+      set(obj, 'content', null);
+
+      assert.equal(obj.length, 0, 'length is 0 without content');
+      assert.deepEqual(obj.content, null, 'content was updated');
+    }
+
+    '@test setting length to 0'(assert) {
+      let obj = ArrayProxy.create({ content: ['foo', 'bar'] });
+
+      assert.equal(obj.length, 2, 'precond');
+
+      set(obj, 'length', 0);
+
+      assert.equal(obj.length, 0, 'length was updated');
+      assert.deepEqual(obj.content, [], 'content length was truncated');
+    }
+
+    '@test setting length to smaller value'(assert) {
+      let obj = ArrayProxy.create({ content: ['foo', 'bar'] });
+
+      assert.equal(obj.length, 2, 'precond');
+
+      set(obj, 'length', 1);
+
+      assert.equal(obj.length, 1, 'length was updated');
+      assert.deepEqual(obj.content, ['foo'], 'content length was truncated');
+    }
+
+    '@test setting length to larger value'(assert) {
+      let obj = ArrayProxy.create({ content: ['foo', 'bar'] });
+
+      assert.equal(obj.length, 2, 'precond');
+
+      assert.throws(function() {
+        set(obj, 'length', 3);
+      }, /Cannot set array proxy length to a larger value/);
+    }
+
+    '@test setting length after content set to null'(assert) {
+      let obj = ArrayProxy.create({ content: ['foo', 'bar'] });
+
+      assert.equal(obj.length, 2, 'precond');
+
+      set(obj, 'content', null);
+      assert.equal(obj.length, 0, 'length was updated');
+
+      set(obj, 'length', 0);
+      assert.equal(obj.length, 0, 'length is still updated');
+    }
+
+    '@test setting length to greater than zero'(assert) {
+      let obj = ArrayProxy.create({ content: ['foo', 'bar'] });
+
+      assert.equal(obj.length, 2, 'precond');
+
+      set(obj, 'length', 1);
+
+      assert.equal(obj.length, 1, 'length was updated');
+      assert.deepEqual(obj.content, ['foo'], 'content length was truncated');
+    }
+
     ['@test array proxy + aliasedProperty complex test'](assert) {
       let aCalled, bCalled, cCalled, dCalled, eCalled;