diff --git a/assembler/assembler.py b/assembler/assembler.py
index 4d36209..8302f94 100644
--- a/assembler/assembler.py
+++ b/assembler/assembler.py
@@ -3,7 +3,7 @@ from collections import deque
 from .context import FileContext
 from .tokenize import Tokenizer, WHITESPACE
 from .opcodes import make_opcodes
-from .util import can_be_mark, can_convert_to_int, autoint
+from .util import can_be_mark, can_convert_to_int, autoint, int16_2_bytes
 from .directives import SetDirective
 
 class ParsingError(Exception): 
@@ -92,7 +92,14 @@ class Assembler(object):
 		# FIXME:
 		# Make this work for tons of data.
 		# Or is that necessary?
-		return file_.write(bytes(self._code_objects))
+		# TODO:
+		# Figure out whether/what improovements are necessary here
+		length = int16_2_bytes(len(self._code_objects))
+		if(len(self._code_objects).bit_length() > 16):
+			raise ValueError("Program size excceeds 2^16.")
+		file_.write(length)
+		for word in self._code_objects:
+			file_.write(int16_2_bytes(word))
 
 
 	def parse_mark(self, token):
diff --git a/assembler/util.py b/assembler/util.py
index 60d043b..e5d4630 100644
--- a/assembler/util.py
+++ b/assembler/util.py
@@ -1,6 +1,7 @@
 """
 Utility functions used for parsing.
 """
+import struct
 
 
 def can_be_mark(argument):
@@ -83,3 +84,11 @@ def autoint(value):
 	return int(value)
 	
 
+def int16_2_bytes(value):
+	"""
+	Return the bytes representation of a 16bit unsigned
+	integer in 8bit words.
+	"""
+	if(value < 0):
+		return struct.pack("<h", value)
+	return struct.pack("<H", value)