diff --git a/src/libcollections/lib.rs b/src/libcollections/lib.rs
index a83804828e8b5..87a15c305e37f 100644
--- a/src/libcollections/lib.rs
+++ b/src/libcollections/lib.rs
@@ -31,7 +31,6 @@ pub use bitv::Bitv;
 pub use btree::BTree;
 pub use deque::Deque;
 pub use dlist::DList;
-pub use enum_set::EnumSet;
 pub use hashmap::{HashMap, HashSet};
 pub use list::List;
 pub use lru_cache::LruCache;
@@ -45,7 +44,6 @@ pub mod bitv;
 pub mod btree;
 pub mod deque;
 pub mod dlist;
-pub mod enum_set;
 pub mod hashmap;
 pub mod list;
 pub mod lru_cache;
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index a86348947f138..5570f145acc4c 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -54,7 +54,7 @@ use syntax::{ast, ast_map};
 use syntax::owned_slice::OwnedSlice;
 use syntax::abi::AbiSet;
 use syntax;
-use collections::enum_set::{EnumSet, CLike};
+use std::enum_set::{EnumSet, CLike};
 
 pub type Disr = u64;
 
diff --git a/src/libserialize/collection_impls.rs b/src/libserialize/collection_impls.rs
index 8631fef5168ab..65ded0f6a2594 100644
--- a/src/libserialize/collection_impls.rs
+++ b/src/libserialize/collection_impls.rs
@@ -17,7 +17,7 @@ use std::hash::{Hash, Hasher};
 use {Decodable, Encodable, Decoder, Encoder};
 use collections::{DList, RingBuf, TreeMap, TreeSet, Deque, HashMap, HashSet,
                   TrieMap, TrieSet};
-use collections::enum_set::{EnumSet, CLike};
+use std::enum_set::{EnumSet, CLike};
 
 impl<
     E,
diff --git a/src/libcollections/enum_set.rs b/src/libstd/enum_set.rs
similarity index 97%
rename from src/libcollections/enum_set.rs
rename to src/libstd/enum_set.rs
index 07f3181d218e5..46cc9b9d9bd8b 100644
--- a/src/libcollections/enum_set.rs
+++ b/src/libstd/enum_set.rs
@@ -1,4 +1,4 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -13,7 +13,10 @@
 //! This module defines a container which uses an efficient bit mask
 //! representation to hold C-like enum variants.
 
-use std::num::Bitwise;
+use num::Bitwise;
+use option::{None, Some, Option};
+use ops::{BitOr,BitAnd,Sub};
+use iter::Iterator;
 
 #[deriving(Clone, Eq, TotalEq, Hash, Show)]
 /// A specialized Set implementation to use enum types.
@@ -137,8 +140,9 @@ impl<E:CLike> Iterator<E> for Items<E> {
 #[cfg(test)]
 mod test {
 
-    use std::cast;
+    use cast;
 
+    use iter::Iterator;
     use enum_set::{EnumSet, CLike};
 
     #[deriving(Eq, Show)]
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index c130b89b6d455..81a73f0b3cc95 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -161,6 +161,7 @@ pub mod any;
 pub mod option;
 pub mod result;
 pub mod cell;
+pub mod enum_set;
 
 
 /* Tasks and communication */