diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/collections/for-in.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/collections/for-in.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,25 @@
+// for-in loops on Maps and Sets enumerate properties.
+
+var test = function test(obj) {
+    assertEq(Object.keys(obj).length, 0);
+
+    var i = 0, v;
+    for (v in obj)
+        i++;
+    assertEq(i, 0);
+
+    obj.ownProp = 1;
+    assertEq(Object.keys(obj).join(), "ownProp");
+
+    for (v in obj)
+        i++;
+    assertEq(i, 1);
+    assertEq(v, "ownProp");
+
+    delete obj.ownProp;
+};
+
+test(Map.prototype);
+test(new Map);
+test(Set.prototype);
+test(new Set);