diff --git a/src/test/run-pass/associated-types-duplicate-binding-in-env-hrtb.rs b/src/test/run-pass/associated-types-duplicate-binding-in-env-hrtb.rs
index f4b765d14b07..8b7ea61dc77e 100644
--- a/src/test/run-pass/associated-types-duplicate-binding-in-env-hrtb.rs
+++ b/src/test/run-pass/associated-types-duplicate-binding-in-env-hrtb.rs
@@ -1,3 +1,17 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Check that we do not report ambiguities when equivalent predicates
+// (modulo bound lifetime names) appears in the environment
+// twice. Issue #21965.
+
 fn foo<T>(t: T) -> i32
     where T : for<'a> Fn(&'a u8) -> i32,
           T : for<'b> Fn(&'b u8) -> i32,