diff -r 000000000000 -r 6474c204b198 js/src/tests/ecma_6/Set/NaN-as-key.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/ecma_6/Set/NaN-as-key.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,56 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+//-----------------------------------------------------------------------------
+var BUGNUMBER = 722260;
+var summary = 'All NaNs must be treated as identical keys for Set';
+
+print(BUGNUMBER + ": " + summary);
+
+/**************
+ * BEGIN TEST *
+ **************/
+
+/* Avoid constant-folding that would happen were |undefined| to be used. */
+var key = -/a/g.missingProperty;
+
+var s = new Set();
+s.add(key, 17);
+assertEq(s.has(key), true);
+assertEq(s.has(-key), true);
+assertEq(s.has(NaN), true);
+
+s.delete(-key);
+assertEq(s.has(key), false);
+assertEq(s.has(-key), false);
+assertEq(s.has(NaN), false);
+
+s.add(-key, 17);
+assertEq(s.has(key), true);
+assertEq(s.has(-key), true);
+assertEq(s.has(NaN), true);
+
+s.delete(NaN);
+assertEq(s.has(key), false);
+assertEq(s.has(-key), false);
+assertEq(s.has(NaN), false);
+
+s.add(NaN, 17);
+assertEq(s.has(key), true);
+assertEq(s.has(-key), true);
+assertEq(s.has(NaN), true);
+
+s.delete(key);
+assertEq(s.has(key), false);
+assertEq(s.has(-key), false);
+assertEq(s.has(NaN), false);
+
+
+/******************************************************************************/
+
+if (typeof reportCompare === "function")
+  reportCompare(true, true);
+
+print("Tests complete");