1 files changed, 2 insertions, 3 deletions
diff --git a/src/librustc/middle/stability.rs b/src/librustc/middle/stability.rs
index 302c11f309d..e65f17c7949 100644
--- a/src/librustc/middle/stability.rs
+++ b/src/librustc/middle/stability.rs
@@ -25,7 +25,7 @@ use crate::util::nodemap::{FxHashSet, FxHashMap};
 use std::mem::replace;
 use std::cmp::Ordering;
 
-#[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Copy, Debug, Eq, Hash)]
+#[derive(PartialEq, Clone, Copy, Debug)]
 pub enum StabilityLevel {
     Unstable,
     Stable,
@@ -905,11 +905,10 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
             // Warn if the user has enabled an already-stable lang feature.
             unnecessary_stable_feature_lint(tcx, span, feature, since);
         }
-        if lang_features.contains(&feature) {
+        if !lang_features.insert(feature) {
             // Warn if the user enables a lang feature multiple times.
             duplicate_feature_err(tcx.sess, span, feature);
         }
-        lang_features.insert(feature);
     }
 
     let declared_lib_features = &tcx.features().declared_lib_features;