diff --git a/spacy/serialize.pyx b/spacy/serialize.pyx
index a5172a556..303b073db 100644
--- a/spacy/serialize.pyx
+++ b/spacy/serialize.pyx
@@ -41,6 +41,37 @@ cdef Code bit_append(Code code, bint bit) nogil:
         code.bits &= ~(one << code.length)
     code.length += 1
     return code
+
+
+cdef class BitArray:
+    cdef int length
+    cdef bytes data
+    cdef unsigned char byte
+    cdef unsigned char bit_of_byte
+    def __init__(self):
+        self.data = b''
+        self.byte = 0
+        self.bit_of_byte = 0
+
+    def as_bytes(self):
+        if self.bit_of_byte != 0:
+            return self.data + chr(self.byte)
+        else:
+            return self.data
+
+    cdef int extend(self, uint64_t code, char n_bits) except -1:
+        cdef uint64_t one = 1
+        cdef unsigned char bit_of_code
+        for bit_of_code in range(n_bits):
+            if code & (one << bit_of_code):
+                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 class HuffmanCodec:
@@ -75,27 +106,11 @@ cdef class HuffmanCodec:
         assign_codes(self.nodes, self.codes, len(self.nodes) - 1, path)
 
     def encode(self, uint32_t[:] sequence):
-        cdef Code code
-        cdef bytes output = b''
-        cdef unsigned char byte = 0
-        cdef uint64_t one = 1
-        cdef unsigned char i_of_byte = 0
-        cdef unsigned char i_of_code = 0
-        for index in list(sequence) + [self.eol]:
-            code = self.codes[index]
-            for i_of_code in range(code.length):
-                if code.bits & (one << i_of_code):
-                    byte |= one << i_of_byte
-                else:
-                    byte &= ~(one << i_of_byte)
-                i_of_byte += 1
-                if i_of_byte == 8:
-                    output += chr(byte)
-                    byte = 0
-                    i_of_byte = 0
-        if i_of_byte != 0:
-            output += chr(byte)
-        return output
+        cdef BitArray 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()
 
     def decode(self, bytes data):
         node = self.nodes.back()