diff --git a/src/librustc_span/lib.rs b/src/librustc_span/lib.rs
index 78661cd61a39..1c3bca6608f5 100644
--- a/src/librustc_span/lib.rs
+++ b/src/librustc_span/lib.rs
@@ -15,6 +15,7 @@
 #![feature(specialization)]
 
 // allow wasm target for rustc-ap-rustc_span
+#[allow(unused)]
 extern crate rustc_macros;
 
 use rustc_data_structures::AtomicRef;