Typo.
diff --git a/Doc/ext/building.tex b/Doc/ext/building.tex
index 3f54b43..42384c1 100644
--- a/Doc/ext/building.tex
+++ b/Doc/ext/building.tex
@@ -8,7 +8,7 @@
extensions and custom interpreters. Starting with Python 2.0, this
mechanism (known as related to Makefile.pre.in, and Setup files) is no
longer supported. Building custom interpreters was rarely used, and
-extensions modules can be built using distutils.
+extension modules can be built using distutils.
Building an extension module using distutils requires that distutils
is installed on the build machine, which is included in Python 2.x and