diff --git a/mini-macro/src/lib.rs b/mini-macro/src/lib.rs
index 60ffd94e733..92b6f701555 100644
--- a/mini-macro/src/lib.rs
+++ b/mini-macro/src/lib.rs
@@ -1,5 +1,7 @@
 #![feature(proc_macro_quote, proc_macro_hygiene)]
 #![deny(rust_2018_idioms)]
+// FIXME: Remove this attribute once the weird failure is gone.
+#![allow(unused_extern_crates)]
 extern crate proc_macro;
 
 use proc_macro::{quote, TokenStream};