diff --git a/Cargo.toml b/Cargo.toml
index 138a6b0..dc3ec25 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,5 +3,8 @@ name = "bit-set"
 version = "0.1.0"
 authors = ["logaritmisk <anders.e.olsson@gmail.com>"]
 
+[dependencies]
+unreachable = "1.0"
+
 [profile.release]
 lto = true
diff --git a/src/hasher.rs b/src/hasher.rs
new file mode 100644
index 0000000..cbba651
--- /dev/null
+++ b/src/hasher.rs
@@ -0,0 +1,32 @@
+use std::default::Default;
+use std::hash::{BuildHasherDefault, Hasher};
+
+use unreachable;
+
+pub 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]) {
+        unsafe { unreachable::unreachable() };
+    }
+
+    #[inline]
+    fn write_u64(&mut self, i: u64) {
+        *self = BitHasher(i);
+    }
+}
+
+pub type BitBuildHasher = BuildHasherDefault<BitHasher>;
diff --git a/src/lib.rs b/src/lib.rs
index 8609b6b..624c8db 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,43 +1,18 @@
+extern crate unreachable;
+
 use std::ops;
 use std::iter::FromIterator;
 use std::default::Default;
-use std::hash::{BuildHasherDefault, Hasher};
 use std::collections::HashMap;
 
+mod hasher;
+
+use hasher::BitBuildHasher;
+
 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>;
-
 type Block = u64;
-type Storage = BitHashMap<u64, Block>;
+type Storage = HashMap<u64, Block, BitBuildHasher>;
 
 #[inline]
 fn block_bit(x: u64, d: u64) -> (u64, u64) {
@@ -60,12 +35,9 @@ impl BitSet {
     }
 
     #[inline]
-    pub fn with_capacity(nbits: usize) -> BitSet {
-        let (mut block, bit) = block_bit(nbits as u64, BITS);
-        block += (bit > 0) as u64;
-
+    pub fn with_capacity(capacity: usize) -> BitSet {
         BitSet {
-            blocks: Storage::with_capacity_and_hasher(block as usize, Default::default()),
+            blocks: Storage::with_capacity_and_hasher(capacity, Default::default()),
             nbits: 0,
         }
     }
@@ -124,8 +96,8 @@ impl BitSet {
         let (block, bit) = block_bit(value, BITS);
 
         match self.blocks.get(&block) {
-            None => false,
             Some(block) => (block & (1 << bit)) != 0,
+            None => false,
         }
     }
 
@@ -180,22 +152,17 @@ impl ops::BitOr for BitSet {
     type Output = Self;
 
     #[inline]
-    fn bitor(self, rhs: Self) -> Self {
-        let mut blocks = self.blocks.clone();
-
+    fn bitor(mut self, rhs: Self) -> Self {
         for (key, value) in &rhs.blocks {
-            *blocks.entry(*key).or_insert(0) |= value;
+            *self.blocks.entry(*key).or_insert(0) |= value;
         }
 
-        let nbits = blocks
+        self.nbits = self.blocks
             .values()
             .map(|block| block.count_ones() as usize)
             .sum();
 
-        BitSet {
-            blocks: blocks,
-            nbits: nbits,
-        }
+        self
     }
 }
 
@@ -203,22 +170,17 @@ impl<'a> ops::BitOr<&'a Self> for BitSet {
     type Output = Self;
 
     #[inline]
-    fn bitor(self, rhs: &'a Self) -> Self {
-        let mut blocks = self.blocks.clone();
-
+    fn bitor(mut self, rhs: &'a Self) -> Self {
         for (key, value) in &rhs.blocks {
-            *blocks.entry(*key).or_insert(0) |= value;
+            *self.blocks.entry(*key).or_insert(0) |= value;
         }
 
-        let nbits = blocks
+        self.nbits = self.blocks
             .values()
             .map(|block| block.count_ones() as usize)
             .sum();
 
-        BitSet {
-            blocks: blocks,
-            nbits: nbits,
-        }
+        self
     }
 }