Index: tests/Zend/JsonTest.php
===================================================================
--- tests/Zend/JsonTest.php	(revision 22219)
+++ tests/Zend/JsonTest.php	(working copy)
@@ -755,6 +755,18 @@
     {
         Zend_Json::decode(' some string ');
     }
+
+    /**
+     * @group ZF-9416
+     * Encoding an iterator using the internal encoder should handle undefined keys
+     */
+    public function testIteratorWithoutDefinedKey()
+    {
+        $inputValue = new ArrayIterator(array('foo'));
+        $encoded = Zend_Json_Encoder::encode($inputValue);
+        $expectedDecoding = '{"__className":"ArrayIterator","0":"foo"}';
+        $this->assertEquals($encoded, $expectedDecoding);
+    }
 }
 
 /**
Index: library/Zend/Json/Encoder.php
===================================================================
--- library/Zend/Json/Encoder.php	(revision 22219)
+++ library/Zend/Json/Encoder.php	(working copy)
@@ -145,7 +145,7 @@
         foreach ($propCollection as $name => $propValue) {
             if (isset($propValue)) {
                 $props .= ','
-                        . $this->_encodeValue($name)
+                        . $this->_encodeString($name)
                         . ':'
                         . $this->_encodeValue($propValue);
             }