--- a/src/jdk/nashorn/internal/runtime/ScriptObject.java	Fri Jun 27 21:54:16 2014 +0530
+++ b/src/jdk/nashorn/internal/runtime/ScriptObject.java	Mon Jun 30 20:23:16 2014 +0530
@@ -691,6 +691,7 @@
         assert isValidArrayIndex(index) : "invalid array index";
         final long longIndex = ArrayIndex.toLongIndex(index);
         doesNotHaveEnsureDelete(longIndex, getArray().length(), false);
+        setArray(getArray().ensure(longIndex));
         setArray(getArray().set(index, value, false));
     }
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/script/basic/JDK-8048718.js	Mon Jun 30 20:23:16 2014 +0530
@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * JDK-8048718: JSON.parse('{"0":0, "64":0}') throws ArrayindexOutOfBoundsException
+ *
+ * @test
+ * @run
+ */
+
+var obj = JSON.parse('{"0":0, "64":0}');
+if ("1" in obj) {
+    fail("found element at index 1");
+}
+
+if ("63" in obj) {
+    fail("found element at index 63");
+}
+
+if (obj[0] != 0) {
+    fail("expected obj[0] to be 0");
+}
+
+if (obj[64] != 0) {
+    fail("expected obj[64] to be 0");
+}
+
+for (var i in obj) {
+    if (i != "0" && i != "64") {
+        fail("invalid property " + i);
+    }
+}