diff --git a/src/libcollections/lib.rs b/src/libcollections/lib.rs
index 9a35ac1f698..0ea8975bbde 100644
--- a/src/libcollections/lib.rs
+++ b/src/libcollections/lib.rs
@@ -38,6 +38,7 @@
 #![feature(unsafe_no_drop_flag, filling_drop)]
 #![feature(step_by)]
 #![feature(str_char)]
+#![feature(str_words)]
 #![feature(slice_patterns)]
 #![feature(debug_builders)]
 #![feature(utf8_error)]
diff --git a/src/librustc_unicode/u_str.rs b/src/librustc_unicode/u_str.rs
index c63c586b6a9..097776312df 100644
--- a/src/librustc_unicode/u_str.rs
+++ b/src/librustc_unicode/u_str.rs
@@ -26,7 +26,8 @@ use core::str::Split;
 use tables::grapheme::GraphemeCat;
 
 /// An iterator over the words of a string, separated by a sequence of whitespace
-#[stable(feature = "rust1", since = "1.0.0")]
+#[unstable(feature = "str_words",
+           reason = "words() will be replaced by split_whitespace() in 1.1.0")]
 pub struct Words<'a> {
     inner: Filter<Split<'a, fn(char) -> bool>, fn(&&str) -> bool>,
 }