diff --git a/idna/codec.py b/idna/codec.py
index ece9bb3..30fe72f 100644
--- a/idna/codec.py
+++ b/idna/codec.py
@@ -67,15 +67,7 @@ def _buffer_decode(self, data, errors, final):
         if not data:
             return ('', 0)
 
-        # IDNA allows decoding to operate on Unicode strings, too.
-        if isinstance(data, unicode):
-            labels = _unicode_dots_re.split(data)
-        else:
-            # Must be ASCII string
-            data = str(data)
-            unicode(data, 'ascii')
-            labels = data.split('.')
-
+        labels = _unicode_dots_re.split(data)
         trailing_dot = ''
         if labels:
             if not labels[-1]:
diff --git a/tests/test_idna_uts46.py b/tests/test_idna_uts46.py
index 2e7ad93..fd1996d 100755
--- a/tests/test_idna_uts46.py
+++ b/tests/test_idna_uts46.py
@@ -1,10 +1,13 @@
 """Tests for TR46 code."""
 
 import os.path
+import re
 import unittest
 
 import idna
 
+_RE_UNICODE = re.compile("\\\\u([0-9a-fA-F]{4})")
+_RE_SURROGATE = re.compile("[\uD800-\uDBFF][\uDC00-\uDFFF]")
 _SKIP_TESTS = [
     # These are strings that are illegal in IDNA 2008. Older versions of the UTS-46 test suite
     # had these denoted with the 'NV8' marker but this has been removed, so we need to manually
@@ -109,8 +112,7 @@ class TestIdnaTest(unittest.TestCase):
     def __init__(self, lineno=None, fields=None):
         super().__init__()
         self.lineno = lineno
-        if fields:
-            self.fields = fields
+        self.fields = fields
 
     def id(self):
         return '{}.{}'.format(super().id(), self.lineno)