--- a/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeArray.java	Mon Nov 28 09:20:13 2016 +0100
+++ b/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/objects/NativeArray.java	Mon Nov 28 09:57:40 2016 +0100
@@ -822,13 +822,12 @@
     private static void concatToList(final ArrayList<Object> list, final Object obj) {
         final boolean isScriptArray  = isArray(obj);
         final boolean isScriptObject = isScriptArray || obj instanceof ScriptObject;
-        if (isScriptArray || obj instanceof Iterable || (obj != null && obj.getClass().isArray())) {
+        if (isScriptArray || obj instanceof Iterable || obj instanceof JSObject || (obj != null && obj.getClass().isArray())) {
             final Iterator<Object> iter = arrayLikeIterator(obj, true);
             if (iter.hasNext()) {
                 for (int i = 0; iter.hasNext(); ++i) {
                     final Object value = iter.next();
-                    final boolean lacksIndex = obj != null && !((ScriptObject)obj).has(i);
-                    if (value == ScriptRuntime.UNDEFINED && isScriptObject && lacksIndex) {
+                    if (value == ScriptRuntime.UNDEFINED && isScriptObject && !((ScriptObject)obj).has(i)) {
                         // TODO: eventually rewrite arrayLikeIterator to use a three-state enum for handling
                         // UNDEFINED instead of an "includeUndefined" boolean with states SKIP, INCLUDE,
                         // RETURN_EMPTY. Until then, this is how we'll make sure that empty elements don't make it
@@ -1828,15 +1827,14 @@
             }
 
             final Object arg = args[2];
-            //args[2] continuousarray or non arraydata, let past non array datas
+            // The generic version uses its own logic and ArrayLikeIterator to decide if an object should
+            // be iterated over or added as single element. To avoid duplication of code and err on the safe side
+            // we only use the specialized version if arg is either a continuous array or a JS primitive.
             if (arg instanceof NativeArray) {
-                final ContinuousArrayData argData = getContinuousArrayData(arg);
-                if (argData == null) {
-                    return false;
-                }
+                return (getContinuousArrayData(arg) != null);
             }
 
-            return true;
+            return JSType.isPrimitive(arg);
         }
     }
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/script/basic/JDK-8161579.js	Mon Nov 28 09:57:40 2016 +0100
@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2016, 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-8161579: Array-like AbstractJSObject-based instance not treated as array by native array functions
+ *
+ * @test
+ * @run
+ */
+
+
+var AbstractJSObject = Java.type("jdk.nashorn.api.scripting.AbstractJSObject");
+var JavaStringArray = Java.type("java.lang.String[]");
+var JavaArrayList = Java.type("java.util.ArrayList");
+
+var arrayLikeJSObject = new AbstractJSObject() {
+    hasMember: function(name) { return name == "length"; },
+    getMember: function(name) { return name == "length" ? 3 : null; },
+    hasSlot: function(slot) { return slot >= 0 && slot <= 2; },
+    getSlot: function(slot) { return "abc"[slot]; },
+    isArray: function() { return true; }
+}
+
+var javaStringArray = new JavaStringArray(3);
+javaStringArray[0] = "x";
+javaStringArray[1] = "y";
+javaStringArray[2] = "z";
+
+var javaArrayList = new JavaArrayList();
+javaArrayList.add("i");
+javaArrayList.add("j");
+javaArrayList.add("k");
+
+Assert.assertEquals([1, 2, 3].concat(arrayLikeJSObject).join(), "1,2,3,a,b,c");
+Assert.assertEquals([1, 2, 3].concat(javaStringArray).join(), "1,2,3,x,y,z");
+Assert.assertEquals([1, 2, 3].concat(javaArrayList).join(), "1,2,3,i,j,k");
+Assert.assertEquals([1, 2, 3].concat("foo").join(), "1,2,3,foo");
+Assert.assertEquals([1, 2, 3].concat(4).join(), "1,2,3,4");
+Assert.assertEquals([1, 2, 3].concat(false).join(), "1,2,3,false");
+