Fix typo.
diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index b44dca4..1bcd376 100644
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -816,7 +816,7 @@
encoding was used for encoding a Unicode string. Each charmap encoding can
decode any random byte sequence. However that's not possible with UTF-8, as
UTF-8 byte sequences have a structure that doesn't allow arbitrary byte
-sequence. To increase the reliability with which a UTF-8 encoding can be
+sequences. To increase the reliability with which a UTF-8 encoding can be
detected, Microsoft invented a variant of UTF-8 (that Python 2.5 calls
``"utf-8-sig"``) for its Notepad program: Before any of the Unicode characters
is written to the file, a UTF-8 encoded BOM (which looks like this as a byte