diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testConstructorArgs-2.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testConstructorArgs-2.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,12 @@
+function f(a, b, c) {
+    this.a = a;
+    assertEq(b, 'x');
+    assertEq(c, void 0);
+}
+
+for (var x = 0; x < 9; ++x) {
+    f.prototype = {};
+    var obj = new f(x, 'x');  // fewer than f.length arguments
+    assertEq(obj.a, x);
+    assertEq(Object.getPrototypeOf(obj), f.prototype);
+}