diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testSetProtoRegeneratesObjectShape.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testSetProtoRegeneratesObjectShape.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+function testSetProtoRegeneratesObjectShape()
+{
+  var f = function() {};
+  var g = function() {};
+  g.prototype.__proto__ = {};
+
+  function iq(obj)
+  {
+    for (var i = 0; i < 10; ++i)
+      "" + obj.prototype;
+  }
+
+  iq(f);
+  iq(f);
+  iq(f);
+  iq(f);
+  iq(g);
+
+  if (shapeOf(f.prototype) === shapeOf(g.prototype))
+    return "object shapes same after proto of one is changed";
+
+  return true;
+}
+assertEq(testSetProtoRegeneratesObjectShape(), true);