Minor grammar fix.
diff --git a/Doc/packaging/setupcfg.rst b/Doc/packaging/setupcfg.rst
index ddec41a..1a394b5 100644
--- a/Doc/packaging/setupcfg.rst
+++ b/Doc/packaging/setupcfg.rst
@@ -72,7 +72,7 @@
---------------
A configuration file can be extended (i.e. included) by other files. For this,
-a ``DEFAULT`` section must contain an ``extends`` key which value points to one
+a ``DEFAULT`` section must contain an ``extends`` key whose value points to one
or more files which will be merged into the current files by adding new sections
and fields. If a file loaded by ``extends`` contains sections or keys that
already exist in the original file, they will not override the previous values.