diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/collections/Set-iterator-add-remove.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/collections/Set-iterator-add-remove.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,13 @@
+// Removing and re-adding entries while an iterator is live causes the iterator to visit them again.
+
+var set = Set(['a']);
+var n = 5;
+for (let v of set) {
+    assertEq(v, 'a');
+    if (n === 0)
+        break;
+    set.delete('a');
+    set.add('a');
+    n--;
+}
+assertEq(n, 0);