diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/debug/Environment-setVariable-07.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/debug/Environment-setVariable-07.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,15 @@
+// setVariable works on let-bindings.
+
+var g = newGlobal();
+function test(code, val) {
+    g.eval("function f() { " + code + " }");
+    var dbg = new Debugger(g);
+    dbg.onDebuggerStatement = function (frame) {
+        frame.environment.setVariable("a", val);
+    };
+    assertEq(g.f(), val);
+}
+
+test("let a = 1; debugger; return a;", "xyzzy");
+test("{ let a = 1; debugger; return a; }", "plugh");
+test("let (a = 1) { debugger; return a; }", "wcgr");