diff --git a/compiler/rustc_abi/src/lib.rs b/compiler/rustc_abi/src/lib.rs
index 3dc548c4554..ea634d7485e 100644
--- a/compiler/rustc_abi/src/lib.rs
+++ b/compiler/rustc_abi/src/lib.rs
@@ -3,6 +3,7 @@
 #![cfg_attr(feature = "nightly", doc(rust_logo))]
 #![cfg_attr(feature = "nightly", feature(rustdoc_internals))]
 #![cfg_attr(feature = "nightly", feature(step_trait))]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 use std::fmt;
diff --git a/compiler/rustc_ast/src/lib.rs b/compiler/rustc_ast/src/lib.rs
index 27e9f3d137f..7730d0b4b78 100644
--- a/compiler/rustc_ast/src/lib.rs
+++ b/compiler/rustc_ast/src/lib.rs
@@ -19,6 +19,7 @@
 #![feature(never_type)]
 #![feature(rustdoc_internals)]
 #![feature(stmt_expr_attributes)]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 pub mod util {
diff --git a/compiler/rustc_ast_ir/src/lib.rs b/compiler/rustc_ast_ir/src/lib.rs
index 1d0c76f6cea..eeed5d36151 100644
--- a/compiler/rustc_ast_ir/src/lib.rs
+++ b/compiler/rustc_ast_ir/src/lib.rs
@@ -2,6 +2,7 @@
 #![cfg_attr(feature = "nightly", allow(internal_features))]
 #![cfg_attr(feature = "nightly", feature(never_type))]
 #![cfg_attr(feature = "nightly", feature(rustc_attrs))]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 #[cfg(feature = "nightly")]