diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/bug639311.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/bug639311.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,18 @@
+/* Avoid use-after-free while sweeping type objects. */
+
+try {
+  Reflparse("")
+} catch(e) {}
+Reflect.parse("for(var a;a;j){if(a%2==0){c()}}")
+try {
+  (function() {
+    for (a = 0;; j) {
+      gc()
+    }
+  })()
+} catch(e) {
+  delete this.Math
+}
+gc()
+Reflect.parse("let(x){}")
+gc()