diff --git a/kdcproxy/codec.py b/kdcproxy/codec.py
index 8942f59..f7e346d 100644
--- a/kdcproxy/codec.py
+++ b/kdcproxy/codec.py
@@ -19,36 +19,11 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
-import os
 import struct
 
+from kdcproxy import parse_pyasn1 as asn1mod
 from kdcproxy.exceptions import ParsingError
 
-ASN1MOD = os.environ.get('KDCPROXY_ASN1MOD')
-
-if ASN1MOD is None:
-    try:
-        from asn1crypto.version import __version_info__ as asn1crypto_version
-    except ImportError:
-        asn1crypto_version = None
-    else:
-        if asn1crypto_version >= (0, 22, 0):
-            ASN1MOD = 'asn1crypto'
-    if ASN1MOD is None:
-        try:
-            __import__('pyasn1')
-        except ImportError:
-            pass
-        else:
-            ASN1MOD = 'pyasn1'
-
-if ASN1MOD == 'asn1crypto':
-    from kdcproxy import parse_asn1crypto as asn1mod
-elif ASN1MOD == 'pyasn1':
-    from kdcproxy import parse_pyasn1 as asn1mod
-else:
-    raise ValueError("Invalid KDCPROXY_ASN1MOD='{}'".format(ASN1MOD))
-
 
 class ProxyRequest(object):
     TYPE = None
diff --git a/kdcproxy/parse_asn1crypto.py b/kdcproxy/parse_asn1crypto.py
deleted file mode 100644
index ac840d0..0000000
--- a/kdcproxy/parse_asn1crypto.py
+++ /dev/null
@@ -1,104 +0,0 @@
-# Copyright (C) 2017, Red Hat, Inc.
-# All rights reserved.
-#
-# Permission is hereby granted, free of charge, to any person obtaining a copy
-# of this software and associated documentation files (the "Software"), to deal
-# in the Software without restriction, including without limitation the rights
-# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-# copies of the Software, and to permit persons to whom the Software is
-# furnished to do so, subject to the following conditions:
-#
-# The above copyright notice and this permission notice shall be included in
-# all copies or substantial portions of the Software.
-#
-# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-# THE SOFTWARE.
-
-from asn1crypto import core
-
-from kdcproxy.exceptions import ASN1ParsingError
-
-
-APPLICATION = 1
-
-
-class KerberosString(core.GeneralString):
-    """KerberosString ::= GeneralString (IA5String)
-
-    For compatibility, implementations MAY choose to accept GeneralString
-    values that contain characters other than those permitted by
-    IA5String...
-    """
-
-
-class Realm(KerberosString):
-    """Realm ::= KerberosString
-    """
-
-
-class ProxyMessage(core.Sequence):
-    pretty_name = 'KDC-PROXY-MESSAGE'
-
-    _fields = [
-        ('kerb-message', core.OctetString, {
-            'explicit': 0}),
-        ('target-domain', Realm, {
-            'explicit': 1, 'optional': True}),
-        ('dclocator-hint', core.Integer, {
-            'explicit': 2, 'optional': True}),
-    ]
-
-
-class ASREQ(core.Sequence):
-    pretty_name = 'AS-REQ'
-
-    explicit = (APPLICATION, 10)
-
-
-class TGSREQ(core.Sequence):
-    pretty_name = 'TGS-REQ'
-
-    explicit = (APPLICATION, 12)
-
-
-class APREQ(core.Sequence):
-    pretty_name = 'AP-REQ'
-
-    explicit = (APPLICATION, 14)
-
-
-class KRBPriv(core.Sequence):
-    pretty_name = 'KRBPRiv'
-
-    explicit = (APPLICATION, 21)
-
-
-def decode_proxymessage(data):
-    req = ProxyMessage.load(data, strict=True)
-    message = req['kerb-message'].native
-    realm = req['target-domain'].native
-    try:  # Python 3.x
-        realm = str(realm, "utf-8")
-    except TypeError:  # Python 2.x
-        realm = str(realm)
-    flags = req['dclocator-hint'].native
-    return message, realm, flags
-
-
-def encode_proxymessage(data):
-    rep = ProxyMessage()
-    rep['kerb-message'] = data
-    return rep.dump()
-
-
-def try_decode(data, cls):
-    try:
-        req = cls.load(data, strict=True)
-    except ValueError as e:
-        raise ASN1ParsingError(e)
-    return req.pretty_name
diff --git a/setup.py b/setup.py
index 6208c5a..cdb5962 100644
--- a/setup.py
+++ b/setup.py
@@ -24,7 +24,7 @@
 from setuptools import setup
 
 install_requires = [
-    'asn1crypto>=0.23',
+    'pyasn1',
     'dnspython'
 ]
 
diff --git a/tests.py b/tests.py
index c2b1fc0..cd82781 100644
--- a/tests.py
+++ b/tests.py
@@ -20,7 +20,6 @@
 # THE SOFTWARE.
 
 import os
-import sys
 import unittest
 from base64 import b64decode
 try:
@@ -226,21 +225,6 @@ def test_kpasswdreq(self):
             'FREEIPA.LOCAL KPASSWD-REQ (603 bytes) (version 0x0001)'
         )
 
-    def test_asn1mod(self):
-        modmap = {
-            'asn1crypto': (
-                'kdcproxy.parse_asn1crypto', 'kdcproxy.parse_pyasn1'),
-            'pyasn1': (
-                'kdcproxy.parse_pyasn1', 'kdcproxy.parse_asn1crypto'),
-        }
-        asn1mod = os.environ.get('KDCPROXY_ASN1MOD', None)
-        if asn1mod is None:
-            self.fail("Tests require KDCPROXY_ASN1MOD env var.")
-        self.assertIn(asn1mod, modmap)
-        mod, opposite = modmap[asn1mod]
-        self.assertIn(mod, set(sys.modules))
-        self.assertNotIn(opposite, set(sys.modules))
-
 
 class KDCProxyConfigTests(unittest.TestCase):
 
diff --git a/tox.ini b/tox.ini
index cca456b..038d996 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,16 +1,11 @@
 [tox]
 minversion = 2.3.1
-envlist = {py36,py37,py38,py39}-{asn1crypto,pyasn1},pep8,py3pep8,doc,coverage-report
+envlist = py36,py37,py38,py39,pep8,py3pep8,doc,coverage-report
 skip_missing_interpreters = true
 
 [testenv]
 deps =
     .[tests]
-    pyasn1: pyasn1
-    asn1crypto: asn1crypto>=0.23
-setenv =
-    asn1crypto: KDCPROXY_ASN1MOD=asn1crypto
-    pyasn1: KDCPROXY_ASN1MOD=pyasn1
 commands =
     {envpython} -m coverage run --parallel \
         -m pytest --capture=no --strict {posargs}