diff --git a/macros/src/lib.rs b/macros/src/lib.rs
index 01a1e31..809d692 100644
--- a/macros/src/lib.rs
+++ b/macros/src/lib.rs
@@ -1,3 +1,5 @@
+#![deny(rust_2018_idioms)]
+
 extern crate gll;
 extern crate proc_macro;
 extern crate proc_quote;
diff --git a/macros/tests/basic.rs b/macros/tests/basic.rs
index 7f5f91c..8f37f5b 100644
--- a/macros/tests/basic.rs
+++ b/macros/tests/basic.rs
@@ -1,3 +1,5 @@
+#![deny(rust_2018_idioms)]
+
 extern crate gll;
 extern crate gll_macros;
 
diff --git a/macros/tests/json.rs b/macros/tests/json.rs
index db8d991..2bfd88b 100644
--- a/macros/tests/json.rs
+++ b/macros/tests/json.rs
@@ -1,3 +1,5 @@
+#![deny(rust_2018_idioms)]
+
 extern crate gll;
 extern crate gll_macros;
 extern crate proc_quote;
diff --git a/src/lib.rs b/src/lib.rs
index 2887caa..3e366af 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,5 @@
 #![deny(unsafe_code)]
+#![deny(rust_2018_idioms)]
 
 extern crate indexing;
 extern crate ordermap;