diff --git a/js/src/jit-test/tests/basic/testBug783543.js b/js/src/jit-test/tests/basic/testBug783543.js
new file mode 100644
index 00000000000..80e3495fc77
--- /dev/null
+++ b/js/src/jit-test/tests/basic/testBug783543.js
@@ -0,0 +1,11 @@
+// |jit-test| error:ReferenceError
+
+try { 
+  evaluate("  (function(c) { const x = 1; for (x in null); })();"); 
+  var expect = "Passed";
+} catch ( e ) {
+  result = expect;
+}
+schedulegc(10);
+eval("var o = new MyObject(); var result = 0; for (var o in foo) { result += this[o]; } ") 
+function MyObject() {}