diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/collections/Map-constructor-3.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/collections/Map-constructor-3.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,9 @@
+// Map can take an argument that is an array of singleton arrays.
+
+var arr = [["a"], ["b"], ["c"]];
+var m = Map(arr);
+assertEq(m.size, 3);
+for (var [k, _] of arr) {
+    assertEq(m.has(k), true);
+    assertEq(m.get(k), undefined);
+}