diff --git a/src/lib.rs b/src/lib.rs
index 92099bd..7a23fe4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,17 +1,47 @@
-extern crate fnv;
-
 use std::ops;
 use std::iter::FromIterator;
+use std::default::Default;
+use std::hash::{Hasher, BuildHasherDefault};
+use std::collections::{HashMap, HashSet};
 
-use fnv::FnvHashMap;
+const BITS: u64 = 64;
+
+struct BitHasher(u64);
+
+impl Default for BitHasher {
+    #[inline]
+    fn default() -> BitHasher {
+        BitHasher(0)
+    }
+}
+
+impl Hasher for BitHasher {
+    #[inline]
+    fn finish(&self) -> u64 {
+        self.0
+    }
+
+    #[inline]
+    fn write(&mut self, _: &[u8]) {
+        panic!("this hasher only works with u64");
+    }
+
+    #[inline]
+    fn write_u64(&mut self, i: u64) {
+        *self = BitHasher(i);
+    }
+}
+
+type BitBuildHasher = BuildHasherDefault<BitHasher>;
+type BitHashMap<K, V> = HashMap<K, V, BitBuildHasher>;
+type BitHashSet<T> = HashSet<T, BitBuildHasher>;
 
-const BITS: usize = 64;
 
 type Block = u64;
-type Storage = FnvHashMap<usize, Block>;
+type Storage = BitHashMap<u64, Block>;
 
 #[inline]
-fn block_bit(x: usize, d: usize) -> (usize, usize) {
+fn block_bit(x: u64, d: u64) -> (u64, u64) {
     (x / d, x % d)
 }
 
@@ -22,6 +52,7 @@ pub struct BitSet {
 }
 
 impl BitSet {
+    #[inline]
     pub fn new() -> BitSet {
         BitSet {
             blocks: Storage::default(),
@@ -29,30 +60,35 @@ impl BitSet {
         }
     }
 
+    #[inline]
     pub fn with_capacity(nbits: usize) -> BitSet {
-        let (mut block, bit) = block_bit(nbits, BITS);
-        block += (bit > 0) as usize;
+        let (mut block, bit) = block_bit(nbits as u64, BITS);
+        block += (bit > 0) as u64;
 
         BitSet {
-            blocks: Storage::with_capacity_and_hasher(block, Default::default()),
+            blocks: Storage::with_capacity_and_hasher(block as usize, Default::default()),
             nbits: 0,
         }
     }
 
+    #[inline]
     pub fn capacity(&self) -> usize {
-        self.blocks.len() * BITS
+        self.blocks.len() * BITS as usize
     }
 
+    #[inline]
     pub fn len(&self) -> usize {
         self.nbits
     }
 
+    #[inline]
     pub fn is_empty(&self) -> bool {
         self.nbits == 0
     }
 
+    #[inline]
     pub fn insert(&mut self, value: usize) -> bool {
-        let (block, bit) = block_bit(value, BITS);
+        let (block, bit) = block_bit(value as u64, BITS);
         let block = self.blocks.entry(block).or_insert(0);
 
         if (*block & (1 << bit)) == 0 {
@@ -65,8 +101,9 @@ impl BitSet {
         }
     }
 
+    #[inline]
     pub fn remove(&mut self, value: usize) -> bool {
-        let (block, bit) = block_bit(value, BITS);
+        let (block, bit) = block_bit(value as u64, BITS);
         let block = self.blocks.entry(block).or_insert(0);
 
         if (*block & (1 << bit)) != 0 {
@@ -79,8 +116,9 @@ impl BitSet {
         }
     }
 
+    #[inline]
     pub fn contains(&self, value: usize) -> bool {
-        let (block, bit) = block_bit(value, BITS);
+        let (block, bit) = block_bit(value as u64, BITS);
 
         match self.blocks.get(&block) {
             None => false,
@@ -113,6 +151,15 @@ impl Extend<usize> for BitSet {
     }
 }
 
+impl<'a> Extend<&'a usize> for BitSet {
+    #[inline]
+    fn extend<I: IntoIterator<Item = &'a usize>>(&mut self, iter: I) {
+        for i in iter {
+            self.insert(*i);
+        }
+    }
+}
+
 impl ops::BitOr for BitSet {
     type Output = Self;