diff --git a/compiler/rustc_lint/src/async_closures.rs b/compiler/rustc_lint/src/async_closures.rs
index 33cc5738262f6..2a821b7110316 100644
--- a/compiler/rustc_lint/src/async_closures.rs
+++ b/compiler/rustc_lint/src/async_closures.rs
@@ -12,6 +12,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
+    /// #![feature(async_closure)]
     /// #![warn(closure_returning_async_block)]
     /// let c = |x: &str| async {};
     /// ```