diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index 27833161ef23d..2c0ef2989c7a6 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -436,7 +436,12 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
             id: LintId::of(INDIRECT_STRUCTURAL_MATCH),
             reference: "issue #62411 <https://github.com/rust-lang/rust/issues/62411>",
             edition: None,
-        }
+        },
+        FutureIncompatibleInfo {
+            id: LintId::of(SOFT_UNSTABLE),
+            reference: "issue #64266 <https://github.com/rust-lang/rust/issues/64266>",
+            edition: None,
+        },
         ]);
 
     // Register renamed and removed lints.
diff --git a/src/test/ui/feature-gates/bench.rs b/src/test/ui/feature-gates/bench.rs
index d8a09625e9639..afe4dc7d54c9b 100644
--- a/src/test/ui/feature-gates/bench.rs
+++ b/src/test/ui/feature-gates/bench.rs
@@ -1,4 +1,5 @@
 #[bench] //~ ERROR use of unstable library feature 'test'
+         //~| WARN this was previously accepted
 fn bench() {}
 
 fn main() {}
diff --git a/src/test/ui/feature-gates/bench.stderr b/src/test/ui/feature-gates/bench.stderr
index 25ddcc5e36169..b9e24e931d42b 100644
--- a/src/test/ui/feature-gates/bench.stderr
+++ b/src/test/ui/feature-gates/bench.stderr
@@ -5,6 +5,8 @@ LL | #[bench]
    |   ^^^^^
    |
    = note: `#[deny(soft_unstable)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
 
 error: aborting due to previous error