diff --git a/src/librustc_data_structures/indexed_vec.rs b/src/librustc_data_structures/indexed_vec.rs
index 622e8c51bee..e2f50c8c889 100644
--- a/src/librustc_data_structures/indexed_vec.rs
+++ b/src/librustc_data_structures/indexed_vec.rs
@@ -416,7 +416,7 @@ impl<I: Idx, T> IndexVec<I, T> {
     }
 
     #[inline]
-    pub fn iter_enumerated(&self) -> Enumerated<I, slice::Iter<T>>
+    pub fn iter_enumerated(&self) -> Enumerated<I, slice::Iter<'_, T>>
     {
         self.raw.iter().enumerate().map(IntoIdx { _marker: PhantomData })
     }
@@ -432,7 +432,7 @@ impl<I: Idx, T> IndexVec<I, T> {
     }
 
     #[inline]
-    pub fn iter_enumerated_mut(&mut self) -> Enumerated<I, slice::IterMut<T>>
+    pub fn iter_enumerated_mut(&mut self) -> Enumerated<I, slice::IterMut<'_, T>>
     {
         self.raw.iter_mut().enumerate().map(IntoIdx { _marker: PhantomData })
     }
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 3a20343033c..8862ba3545e 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -31,6 +31,7 @@
 #![feature(i128)]
 #![feature(conservative_impl_trait)]
 #![feature(specialization)]
+#![feature(underscore_lifetimes)]
 
 #![cfg_attr(unix, feature(libc))]
 #![cfg_attr(test, feature(test))]