Fix typo.
diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index 4554b1e..63895bc 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -246,7 +246,7 @@
Flush and close this stream. This method has no effect if the file is
already closed. Once the file is closed, any operation on the file
- (e.g. reading or writing) will raise an :exc:`ValueError`.
+ (e.g. reading or writing) will raise a :exc:`ValueError`.
As a convenience, it is allowed to call this method more than once;
only the first call, however, will have an effect.