diff --git a/spacy/serialize.pyx b/spacy/serialize.pyx
index 07f9a95f8..15053b4d4 100644
--- a/spacy/serialize.pyx
+++ b/spacy/serialize.pyx
@@ -11,6 +11,8 @@ import numpy
 
 cimport cython
 
+ctypedef unsigned char uchar
+
 # Format
 # - Total number of bytes in message (32 bit int)
 # - Words, terminating in an EOL symbol, huffman coded ~12 bits per word
@@ -33,14 +35,29 @@ cdef Code bit_append(Code code, bint bit) nogil:
 
 
 cdef class BitArray:
-    cdef int length
     cdef bytes data
     cdef unsigned char byte
     cdef unsigned char bit_of_byte
+    cdef uint32_t i
     def __init__(self):
         self.data = b''
         self.byte = 0
         self.bit_of_byte = 0
+        self.i = 0
+
+    def __iter__(self):
+        cdef uchar byte, i
+        cdef uchar one = 1
+        start_byte = self.i // 8
+        if (self.i % 8) != 0:
+            for i in range(self.i % 8):
+                yield (self.data[start_byte] & (one << i))
+            start_byte += 1
+        for byte in self.data[start_byte:]:
+            for i in range(8):
+                yield byte & (one << i)
+        for i in range(self.bit_of_byte):
+            yield self.byte & (one << i)
 
     def as_bytes(self):
         if self.bit_of_byte != 0:
@@ -48,6 +65,18 @@ cdef class BitArray:
         else:
             return self.data
 
+    def append(self, bint bit):
+        cdef uint64_t one = 1
+        if bit:
+            self.byte |= one << self.bit_of_byte
+        else:
+            self.byte &= ~(one << self.bit_of_byte)
+        self.bit_of_byte += 1
+        if self.bit_of_byte == 8:
+            self.data += chr(self.byte)
+            self.byte = 0
+            self.bit_of_byte = 0
+
     cdef int extend(self, uint64_t code, char n_bits) except -1:
         cdef uint64_t one = 1
         cdef unsigned char bit_of_code
@@ -91,31 +120,28 @@ cdef class HuffmanCodec:
         path.length = 0
         assign_codes(self.nodes, self.codes, len(self.nodes) - 1, path)
 
-    def encode(self, uint32_t[:] sequence):
-        cdef BitArray bits = BitArray()
+    def encode(self, uint32_t[:] sequence, BitArray bits=None):
+        if bits is None:
+            bits = BitArray()
         for i in sequence:
             bits.extend(self.codes[i].bits, self.codes[i].length) 
         bits.extend(self.codes[self.eol].bits, self.codes[self.eol].length)
-        return bits.as_bytes()
+        return bits
 
-    def decode(self, bytes data):
+    def decode(self, BitArray bits):
         node = self.nodes.back()
         symbols = [] 
-        cdef unsigned char byte
-        cdef unsigned char i = 0
-        cdef unsigned char one = 1
-        for byte in data:
-            for i in range(8):
-                branch = node.right if (byte & (one << i)) else node.left
-                if branch >= 0:
-                    node = self.nodes.at(branch)
+        for bit in bits:
+            branch = node.right if bit else node.left
+            if branch >= 0:
+                node = self.nodes.at(branch)
+            else:
+                symbol = -(branch + 1)
+                if symbol == self.eol:
+                    return symbols
                 else:
-                    symbol = -(branch + 1)
-                    if symbol == self.eol:
-                        return symbols
-                    else:
-                        symbols.append(symbol)
-                    node = self.nodes.back()
+                    symbols.append(symbol)
+                node = self.nodes.back()
         return symbols
 
     property strings: