diff --git a/Lib/imp.py b/Lib/imp.py
index 31f8c76..a6f6fc8 100644
--- a/Lib/imp.py
+++ b/Lib/imp.py
@@ -225,7 +225,7 @@
 
     """
     suffix, mode, type_ = details
-    if mode and (not mode.startswith(('r', 'U')) or '+' in mode):
+    if mode and (not mode.startswith('r') or '+' in mode):
         raise ValueError('invalid file open mode {!r}'.format(mode))
     elif file is None and type_ in {PY_SOURCE, PY_COMPILED}:
         msg = 'file object required for import (type code {})'.format(type_)