diff --git a/tests/testsuite/main.rs b/tests/testsuite/main.rs
index 50a3e299ab9..8cff78e7f33 100644
--- a/tests/testsuite/main.rs
+++ b/tests/testsuite/main.rs
@@ -1,4 +1,5 @@
-#![warn(rust_2018_idioms)] // while we're getting used to 2018
+// See src/cargo/lib.rs for notes on these lint settings.
+#![warn(rust_2018_idioms)]
 #![allow(clippy::all)]
 #![warn(clippy::needless_borrow)]
 #![warn(clippy::redundant_clone)]