Consistency check for versionadded/changed directives.
diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index 0826ebd..96a4970 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -301,7 +301,7 @@
       Return the new absolute position.
 
       .. versionadded:: 3.1
-         The ``SEEK_*`` constants
+         The ``SEEK_*`` constants.
 
    .. method:: seekable()