diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 02fdc1ae6685e..8ffd00d1b2e60 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -21,6 +21,7 @@
 #![feature(let_chains)]
 #![feature(rustc_attrs)]
 #![feature(rustdoc_internals)]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 use std::cell::{Cell, RefCell};