diff --git a/packages/ember-runtime/lib/computed/reduce_computed_macros.js b/packages/ember-runtime/lib/computed/reduce_computed_macros.js
index 8802584d24c..99251315a9b 100644
--- a/packages/ember-runtime/lib/computed/reduce_computed_macros.js
+++ b/packages/ember-runtime/lib/computed/reduce_computed_macros.js
@@ -740,10 +740,6 @@ function propertySort(itemsKey, sortPropertiesKey) {
       activeObservers.forEach(args => removeObserver(...args));
     }
 
-    let itemsKeyIsAtThis = (itemsKey === '@this');
-    let items = itemsKeyIsAtThis ? this : get(this, itemsKey);
-    if (!isArray(items)) { return emberA(); }
-
     function sortPropertyDidChange() {
       this.notifyPropertyChange(key);
     }
@@ -757,6 +753,10 @@ function propertySort(itemsKey, sortPropertiesKey) {
 
     activeObserversMap.set(this, activeObservers);
 
+    let itemsKeyIsAtThis = (itemsKey === '@this');
+    let items = itemsKeyIsAtThis ? this : get(this, itemsKey);
+    if (!isArray(items)) { return emberA(); }
+
     return sortByNormalizedSortProperties(items, normalizedSortProperties);
   }, { dependentKeys: [`${sortPropertiesKey}.[]`], readOnly: true });
 
diff --git a/packages/ember-runtime/tests/computed/reduce_computed_macros_test.js b/packages/ember-runtime/tests/computed/reduce_computed_macros_test.js
index 7c13a55d879..c0249b97968 100644
--- a/packages/ember-runtime/tests/computed/reduce_computed_macros_test.js
+++ b/packages/ember-runtime/tests/computed/reduce_computed_macros_test.js
@@ -918,6 +918,13 @@ QUnit.test('updating sort properties detaches observers for old sort properties'
   ], 'after changing removed item array is not updated');
 });
 
+QUnit.test('sort works if array property is null (non array value) on first evaluation of computed prop', function() {
+  obj.set('items', null);
+  deepEqual(obj.get('sortedItems'), []);
+  obj.set('items', emberA([{fname: 'Cersei', lname: 'Lanister'}]));
+  deepEqual(obj.get('sortedItems'), [{fname: 'Cersei', lname: 'Lanister'}]);
+});
+
 QUnit.test('updating sort properties updates the sorted array', function() {
   deepEqual(obj.get('sortedItems').mapBy('fname'), [
     'Cersei',