diff --git a/test/mjsunit/regress/regress-5085.js b/test/mjsunit/regress/regress-5085.js
new file mode 100644
index 0000000..0ed034d
--- /dev/null
+++ b/test/mjsunit/regress/regress-5085.js
@@ -0,0 +1,14 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+function foo(x) {
+  return x instanceof Proxy;
+}
+
+assertFalse(foo({}));
+assertFalse(foo({}));
+%OptimizeFunctionOnNextCall(foo);
+assertFalse(foo({}));