#4764 in io.open, set IOError.filename when trying to open a directory on POSIX platforms
diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index c978779..d8cf415 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -109,6 +109,7 @@
             _fileio._FileIO('.', 'r')
         except IOError as e:
             self.assertNotEqual(e.errno, 0)
+            self.assertEqual(e.filename, ".")
         else:
             self.fail("Should have raised IOError")