Issue #14874: Restore charmap decoding speed to pre-PEP 393 levels.
Patch by Serhiy Storchaka.
diff --git a/Lib/encodings/iso8859_1.py b/Lib/encodings/iso8859_1.py
index 8cfc01f..d9cc516 100644
--- a/Lib/encodings/iso8859_1.py
+++ b/Lib/encodings/iso8859_1.py
@@ -301,6 +301,7 @@
     '\xfd'     #  0xFD -> LATIN SMALL LETTER Y WITH ACUTE
     '\xfe'     #  0xFE -> LATIN SMALL LETTER THORN (Icelandic)
     '\xff'     #  0xFF -> LATIN SMALL LETTER Y WITH DIAERESIS
+    '\ufffe'   ## Widen to UCS2 for optimization
 )
 
 ### Encoding table