diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index 9fc17e458a7a0..c704fdb4a3c57 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -70,12 +70,15 @@ use util::nodemap::{NodeMap, NodeSet, DefIdMap, DefIdSet};
 use util::nodemap::FnvHashMap;
 use util::num::ToPrimitive;
 
+use rustc_data_structures::bitset::{U8BitSet, BitSet, BitSetIter};
+
 use arena::TypedArena;
 use std::borrow::{Borrow, Cow};
 use std::cell::{Cell, RefCell, Ref};
 use std::cmp;
 use std::fmt;
 use std::hash::{Hash, SipHasher, Hasher};
+use std::mem;
 use std::ops;
 use std::rc::Rc;
 use std::vec::IntoIter;
@@ -2059,20 +2062,20 @@ pub struct ExistentialBounds<'tcx> {
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub struct BuiltinBounds {
-    bits: u8
+    bit_set: U8BitSet
 }
 
 impl BuiltinBounds {
     pub fn empty() -> BuiltinBounds {
-        BuiltinBounds { bits: 0 }
+        BuiltinBounds { bit_set: BitSet::empty() }
     }
 
     pub fn insert(&mut self, bound: BuiltinBound) {
-        self.bits |= 1 << (bound as u8);
+        self.bit_set.insert(bound as u8)
     }
 
     pub fn contains(&self, bound: BuiltinBound) -> bool {
-        ((self.bits >> (bound as u8)) & 1) == 1
+        self.bit_set.contains(bound as u8)
     }
 
     pub fn iter(&self) -> BuiltinBoundsIter {
@@ -2080,7 +2083,7 @@ impl BuiltinBounds {
     }
 
     fn is_empty(&self) -> bool {
-        self.bits == 0
+        self.bit_set.is_empty()
     }
 
     pub fn to_predicates<'tcx>(&self,
@@ -2095,36 +2098,19 @@ impl BuiltinBounds {
     }
 
     pub fn is_superset(&self, other: &BuiltinBounds) -> bool {
-        (self.bits & other.bits) == other.bits
+        self.bit_set.is_superset(other.bit_set)
     }
 }
 
 pub struct BuiltinBoundsIter {
-    bounds: BuiltinBounds,
-    index: u8
+    bit_set: BitSetIter<u8>
 }
 
 impl Iterator for BuiltinBoundsIter {
     type Item = BuiltinBound;
 
     fn next(&mut self) -> Option<BuiltinBound> {
-        while self.index < 4 {
-            let result = match self.index {
-                0 if self.bounds.contains(BuiltinBound::Send) => Some(BuiltinBound::Send),
-                1 if self.bounds.contains(BuiltinBound::Sized) => Some(BuiltinBound::Sized),
-                2 if self.bounds.contains(BuiltinBound::Copy) => Some(BuiltinBound::Copy),
-                3 if self.bounds.contains(BuiltinBound::Sync) => Some(BuiltinBound::Sync),
-                _ => None
-            };
-
-            self.index += 1;
-
-            if result.is_some() {
-                return result;
-            }
-        }
-
-        return None;
+        self.bit_set.next().map(|b| unsafe { mem::transmute(b) })
     }
 }
 
@@ -2133,10 +2119,11 @@ impl<'a> IntoIterator for &'a BuiltinBounds {
     type IntoIter = BuiltinBoundsIter;
 
     fn into_iter(self) -> BuiltinBoundsIter {
-        BuiltinBoundsIter { bounds: self.clone(), index: 0 }
+        BuiltinBoundsIter { bit_set: self.bit_set.into_iter() }
     }
 }
 
+#[repr(u8)]
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, RustcDecodable, RustcEncodable, Hash, Debug)]
 pub enum BuiltinBound {
     Send,
diff --git a/src/librustc_data_structures/bitset.rs b/src/librustc_data_structures/bitset.rs
new file mode 100644
index 0000000000000..ffd2e9f99a227
--- /dev/null
+++ b/src/librustc_data_structures/bitset.rs
@@ -0,0 +1,96 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::ops::{Add, Sub, Shl, Shr, BitAnd, BitOr};
+use std::num::{Zero, One};
+use std::cmp::PartialEq;
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+pub struct BitSet<N> {
+    bits: N
+}
+
+pub trait UnsignedInt : Zero
+                  + One
+                  + Add<Self, Output=Self>
+                  + Sub<Self, Output=Self>
+                  + Shl<Self, Output=Self>
+                  + Shr<Self, Output=Self>
+                  + BitAnd<Self, Output=Self>
+                  + BitOr<Self, Output=Self>
+                  + PartialEq<Self>
+                  + PartialOrd<Self>
+                  + Copy {}
+
+impl UnsignedInt for u8 {}
+
+pub type U8BitSet = BitSet<u8>;
+
+impl<N: UnsignedInt> BitSet<N> {
+    pub fn empty() -> BitSet<N> {
+        BitSet { bits: Zero::zero() }
+    }
+
+    pub fn insert(&mut self, value: N) {
+        self.bits = self.bits | (N::one() << value);
+    }
+
+    pub fn contains(&self, value: N) -> bool {
+        ((self.bits >> value) & N::one()) == N::one()
+    }
+
+    pub fn iter(&self) -> BitSetIter<N> {
+        self.into_iter()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.bits == N::zero()
+    }
+
+    pub fn is_superset(&self, other: BitSet<N>) -> bool {
+        (self.bits & other.bits) == other.bits
+    }
+}
+
+pub struct BitSetIter<N> {
+    bits: N,
+    index: N
+}
+
+impl<N: UnsignedInt> Iterator for BitSetIter<N> {
+    type Item = N;
+
+    fn next(&mut self) -> Option<N> {
+        if self.bits == N::zero() {
+            return None;
+        }
+
+        while (self.bits & N::one()) == N::zero() {
+            self.index = self.index + N::one();
+            self.bits  = self.bits >> N::one();
+        }
+
+        let result = self.index;
+
+        self.index = self.index + N::one();
+        self.bits = self.bits >> N::one();
+        Some(result)
+    }
+}
+
+
+impl<'a, N: UnsignedInt> IntoIterator for &'a BitSet<N> {
+    type Item = N;
+    type IntoIter = BitSetIter<N>;
+
+    fn into_iter(self) -> BitSetIter<N> {
+        BitSetIter { bits: self.bits, index: N::zero() }
+    }
+}
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 1f8f7694ff90d..ac6821fa8e28c 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -28,6 +28,7 @@
       html_root_url = "http://doc.rust-lang.org/nightly/")]
 
 #![feature(rustc_private, staged_api)]
+#![feature(zero_one)]
 #![cfg_attr(test, feature(test))]
 
 #[macro_use] extern crate log;
@@ -36,4 +37,5 @@ extern crate serialize as rustc_serialize; // used by deriving
 pub mod snapshot_vec;
 pub mod graph;
 pub mod bitvec;
+pub mod bitset;
 pub mod unify;