diff --git a/src/lib.rs b/src/lib.rs
index e21dca7adc1b..8d754bad1b3c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,4 @@
 #![feature(rustc_private)]
-#![feature(map_first_last)]
 #![feature(map_try_insert)]
 #![feature(never_type)]
 #![feature(try_blocks)]