diff --git a/src/org/mozilla/javascript/Hashtable.java b/src/org/mozilla/javascript/Hashtable.java
index 586a8ae3d3..abf6603a19 100644
--- a/src/org/mozilla/javascript/Hashtable.java
+++ b/src/org/mozilla/javascript/Hashtable.java
@@ -55,6 +55,8 @@ public static final class Entry
             if ((k instanceof Number) && ( ! ( k instanceof Double))) {
                 // Hash comparison won't work if we don't do this
                 this.key = ((Number)k).doubleValue();
+            } else if (k instanceof ConsString) {
+                this.key = k.toString();
             } else {
                 this.key = k;
             }
diff --git a/testsrc/jstests/es6/map.js b/testsrc/jstests/es6/map.js
index b154eb567e..e7d3689124 100644
--- a/testsrc/jstests/es6/map.js
+++ b/testsrc/jstests/es6/map.js
@@ -34,4 +34,46 @@ function logElement(value, key, m) {
   assertEquals("c) map[key1] = '' map[key2] = 'undefined' map[key3] = 'undefined' map[key4] = 'null' ", res);
 })();
 
+(function TestGetConcatenatedStrings() {
+  var myMap = new Map([['key1', 'value1'], ['key2', 17]]);
+  for(let i = 1; i <= 1; i++) {
+    let key = 'key' + i;
+
+    assertEquals("value1", myMap.get(key));
+    assertEquals("value1", myMap.get('key1'));
+  }
+})();
+
+(function TestSetConcatenatedStrings() {
+  var myMap = new Map([['key1', 'value1'], ['key2', 17]]);
+  for(let i = 1; i <= 1; i++) {
+    let key = 'key' + i;
+
+    myMap.set(key, 'value2')
+    assertEquals("value2", myMap.get(key));
+    assertEquals("value2", myMap.get('key1'));
+  }
+})();
+
+(function TestHasConcatenatedStrings() {
+  var myMap = new Map([['key1', 'value1'], ['key2', 17]]);
+  for(let i = 1; i <= 1; i++) {
+    let key = 'key' + i;
+
+    assertTrue(myMap.has(key));
+    assertTrue(myMap.has('key1'));
+  }
+})();
+
+(function TestDeleteConcatenatedStrings() {
+  var myMap = new Map([['key1', 'value1'], ['key2', 17]]);
+  for(let i = 1; i <= 1; i++) {
+    let key = 'key' + i;
+
+    assertEquals(2, myMap.size);
+    myMap.delete(key)
+    assertEquals(1, myMap.size);
+  }
+})();
+
 "success";
\ No newline at end of file
diff --git a/testsrc/jstests/es6/set.js b/testsrc/jstests/es6/set.js
new file mode 100644
index 0000000000..978035520f
--- /dev/null
+++ b/testsrc/jstests/es6/set.js
@@ -0,0 +1,66 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+load("testsrc/assert.js");
+
+res = "";
+
+function logElement(value, key) {
+    res += "set[" + key + "] "; 
+}
+
+(function TestForEach() {
+  res = "a) ";
+  var mySet = new Set(['key1', 17]);
+  mySet.forEach(logElement);
+
+  assertEquals("a) set[key1] set[17] ", res);
+})();
+
+(function TestForEachNoKey() {
+  res = "b) ";
+  var mySet = new Set(['', undefined, null, 19]);
+  mySet.forEach(logElement);
+
+  assertEquals("b) set[] set[undefined] set[null] set[19] ", res);
+})();
+
+(function TestAddConcatenatedStrings() {
+  var mySet = new Set(['key1']);
+  var mySet2 = new Set(['key2']);
+  for(let i = 1; i <= 1; i++) {
+    let key = 'key' + i;
+
+    assertEquals(1, mySet.size);
+    mySet.add(key)
+    assertEquals(1, mySet.size);
+
+    assertEquals(1, mySet2.size);
+    mySet2.add(key)
+    assertEquals(2, mySet2.size);
+  }
+})();
+
+(function TestHasConcatenatedStrings() {
+  var mySet = new Set(['key1', 'key2']);
+  for(let i = 1; i <= 1; i++) {
+    let key = 'key' + i;
+
+    assertTrue(mySet.has(key));
+    assertTrue(mySet.has('key1'));
+  }
+})();
+
+(function TestDeleteConcatenatedStrings() {
+  var mySet = new Set(['key1', 'key2']);
+  for(let i = 1; i <= 1; i++) {
+    let key = 'key' + i;
+
+    assertEquals(2, mySet.size);
+    mySet.delete(key)
+    assertEquals(1, mySet.size);
+  }
+})();
+
+"success";
\ No newline at end of file
diff --git a/testsrc/org/mozilla/javascript/tests/es6/NativeSetTest.java b/testsrc/org/mozilla/javascript/tests/es6/NativeSetTest.java
new file mode 100644
index 0000000000..e8c0011c53
--- /dev/null
+++ b/testsrc/org/mozilla/javascript/tests/es6/NativeSetTest.java
@@ -0,0 +1,16 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.javascript.tests.es6;
+
+import org.mozilla.javascript.Context;
+import org.mozilla.javascript.drivers.LanguageVersion;
+import org.mozilla.javascript.drivers.RhinoTest;
+import org.mozilla.javascript.drivers.ScriptTestsBase;
+
+@RhinoTest("testsrc/jstests/es6/set.js")
+@LanguageVersion(Context.VERSION_ES6)
+public class NativeSetTest extends ScriptTestsBase
+{
+}