diff --git a/ox/fixunicode.py b/ox/fixunicode.py
index 3d8d1e8..b49e277 100644
--- a/ox/fixunicode.py
+++ b/ox/fixunicode.py
@@ -6,7 +6,7 @@ from __future__ import print_function
 
 import unicodedata
 
-from six import unichr
+from six import unichr, PY3
 
 __all__ = ['fix_bad_unicode']
 
@@ -75,7 +75,7 @@ def fix_bad_unicode(text):
         >>> fix_bad_unicode('This text was never Unicode at all\x85')
         'This text was never Unicode at all…'
     """
-    if not isinstance(text, str):
+    if isinstance(text, bytes):
         raise TypeError("This isn't even decoded into Unicode yet. "
                         "Decode it first.")
     if len(text) == 0:
@@ -151,7 +151,10 @@ def text_badness(text):
     - Improbable single-byte characters, such as ƒ or ¬
     - Letters in somewhat rare scripts
     '''
-    assert isinstance(text, str)
+    if PY3:
+        assert isinstance(text, str)
+    else:
+        assert isinstance(text, unicode)
     errors = 0
     very_weird_things = 0
     weird_things = 0