diff --git a/Lib/codecs.py b/Lib/codecs.py
index 557ccf7..a67240a 100644
--- a/Lib/codecs.py
+++ b/Lib/codecs.py
@@ -858,10 +858,15 @@
         parameter.
 
     """
-    if encoding is not None and \
-       'b' not in mode:
-        # Force opening of the file in binary mode
-        mode = mode + 'b'
+    if encoding is not None:
+        if 'U' in mode:
+            # No automatic conversion of '\n' is done on reading and writing
+            mode = mode.strip().replace('U', '')
+            if mode[:1] not in set('rwa'):
+                mode = 'r' + mode
+        if 'b' not in mode:
+            # Force opening of the file in binary mode
+            mode = mode + 'b'
     file = __builtin__.open(filename, mode, buffering)
     if encoding is None:
         return file