diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index bacfa0bbfce4f..895268f96c8a8 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -439,13 +439,19 @@ fn mk_test_module(cx: &mut TestCtxt) -> (P<ast::Item>, Option<ast::ViewItem>) {
     let item_ = ast::ItemMod(testmod);
 
     let mod_ident = token::gensym_ident("__test");
+    let allow_unstable = {
+        let unstable = P(nospan(ast::MetaWord(InternedString::new("unstable"))));
+        let allow = P(nospan(ast::MetaList(InternedString::new("allow"),
+                                           vec![unstable])));
+        attr::mk_attr_inner(attr::mk_attr_id(), allow)
+    };
     let item = ast::Item {
         ident: mod_ident,
-        attrs: Vec::new(),
         id: ast::DUMMY_NODE_ID,
         node: item_,
         vis: ast::Public,
         span: DUMMY_SP,
+        attrs: vec![allow_unstable],
     };
     let reexport = cx.reexport_test_harness_main.as_ref().map(|s| {
         // building `use <ident> = __test::main`
diff --git a/src/test/run-pass/issue-20823.rs b/src/test/run-pass/issue-20823.rs
new file mode 100644
index 0000000000000..73b7fc264a529
--- /dev/null
+++ b/src/test/run-pass/issue-20823.rs
@@ -0,0 +1,16 @@
+// 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.
+
+// compile-flags: --test
+
+#![deny(unstable)]
+
+#[test]
+fn foo() {}