diff --git a/src/tools/rustdoc/Cargo.toml b/src/tools/rustdoc/Cargo.toml
index d3881500441..36aa5916da7 100644
--- a/src/tools/rustdoc/Cargo.toml
+++ b/src/tools/rustdoc/Cargo.toml
@@ -2,6 +2,7 @@
 name = "rustdoc-tool"
 version = "0.0.0"
 authors = ["The Rust Project Developers"]
+edition = "2018"
 
 # Cargo adds a number of paths to the dylib search path on windows, which results in
 # the wrong rustdoc being executed. To avoid the conflicting rustdocs, we name the "tool"
diff --git a/src/tools/rustdoc/main.rs b/src/tools/rustdoc/main.rs
index df9d2c6ba96..8bdc365c4ca 100644
--- a/src/tools/rustdoc/main.rs
+++ b/src/tools/rustdoc/main.rs
@@ -1,3 +1,5 @@
+#![deny(rust_2018_idioms)]
+
 #![feature(link_args)]
 
 #[allow(unused_attributes)]
@@ -10,6 +12,4 @@
 // See src/rustc/rustc.rs for the corresponding rustc settings.
 extern {}
 
-extern crate rustdoc;
-
 fn main() { rustdoc::main() }