diff --git a/unicodecsv/py3.py b/unicodecsv/py3.py
index 13a8bf7..42cecce 100644
--- a/unicodecsv/py3.py
+++ b/unicodecsv/py3.py
@@ -48,7 +48,13 @@ def __init__(self, f, dialect=None, encoding='utf-8', errors='strict',
                         for kwd_name in kwds.keys()]):
                 dialect = csv.excel
 
-        f = (bs.decode(encoding, errors=errors) for bs in f)
+        def _safe_decode(bs):
+            if not isinstance(bs, str):
+                return bs.decode(encoding, errors=errors)
+            else:
+                return bs
+
+        f = (_safe_decode(bs) for bs in f)
         self.reader = csv.reader(f, dialect, **kwds)
 
     def __next__(self):