diff --git a/pasn1.py b/pasn1.py
index ef50393..5bfbb5d 100644
--- a/pasn1.py
+++ b/pasn1.py
@@ -77,17 +77,29 @@ class TestSplitFloat(unittest.TestCase):
 		    (0x1fa8c3b094adf1, 971) ]:
 			self.assertEqual(_splitfloat(a * 2**b), (a, b))
 
-class ASN1Object:
-	def __init__(self, tag):
-		self._tag = tag
-
 class ASN1Coder(object):
 	'''A class that contains an PASN.1 encoder/decoder.
 
 	Exports two methods, loads and dumps.'''
 
-	def __init__(self):
-		pass
+	def __init__(self, coerce=None):
+		'''If the arg coerce is provided, when dumping the object,
+		if the type is not found, the coerce function will be called
+		with the obj.  It is expected to return a tuple of a string
+		and an object that has the method w/ the string as defined:
+			'bool': __nonzero__
+			'dict': iteritems
+			'float': compatible w/ float
+			'int': compatible w/ int
+			'list': __iter__
+			'set': __iter__
+			'bytes': __str__
+			'null': no method needed
+			'unicode': encode method returns UTF-8 encoded bytes
+			'datetime': strftime and microsecond
+		'''
+
+		self.coerce = coerce
 
 	_typemap = {
 		bool: 'bool',
@@ -189,14 +201,6 @@ class ASN1Coder(object):
 
 		return r, vend
 
-	def enc_set(self, obj):
-		r = ''.join(self.dumps(x) for x in obj)
-		return _encodelen(len(r)) + r
-
-	def dec_set(self, d, pos, end):
-		r, end = self.dec_list(d, pos, end)
-		return set(r), end
-
 	def enc_list(self, obj):
 		r = ''.join(self.dumps(x) for x in obj)
 		return _encodelen(len(r)) + r
@@ -213,9 +217,15 @@ class ASN1Coder(object):
 
 		return r, vend
 
+	enc_set = enc_list
+
+	def dec_set(self, d, pos, end):
+		r, end = self.dec_list(d, pos, end)
+		return set(r), end
+
 	@staticmethod
 	def enc_bytes(obj):
-		return _encodelen(len(obj)) + obj
+		return _encodelen(len(obj)) + bytes(obj)
 
 	@staticmethod
 	def dec_bytes(d, pos, end):
@@ -311,7 +321,14 @@ class ASN1Coder(object):
 	def dumps(self, obj):
 		'''Convert obj into a string.'''
 
-		tf = self._typemap[type(obj)]
+		try:
+			tf = self._typemap[type(obj)]
+		except KeyError:
+			if self.coerce is None:
+				raise
+
+			tf, obj = self.coerce(obj)
+
 		fun = getattr(self, 'enc_%s' % tf)
 		return self._typetag[tf] + fun(obj)
 
@@ -520,5 +537,39 @@ class TestCode(unittest.TestCase):
 		out = dumps(tobj)
 		self.assertEqual(tobj, loads(out))
 
+	def test_coerce(self):
+		class Foo:
+			pass
+
+		class Bar:
+			pass
+
+		class Baz:
+			pass
+		def coerce(obj):
+			if isinstance(obj, Foo):
+				return 'list', obj.lst
+			elif isinstance(obj, Baz):
+				return 'bytes', obj.s
+
+			raise TypeError('unknown type')
+
+		ac = ASN1Coder(coerce)
+
+		v = [1, 2, 3]
+		o = Foo()
+		o.lst = v
+
+		self.assertEqual(ac.loads(ac.dumps(o)), v)
+		self.assertRaises(TypeError, ac.dumps, Bar())
+
+		v = u'oiejfd'
+		o = Baz()
+		o.s = v
+
+		es = ac.dumps(o)
+		self.assertEqual(ac.loads(es), v)
+		self.assertIsInstance(es, bytes)
+
 	def test_loads(self):
 		self.assertRaises(ValueError, loads, '\x00\x02\x00')