diff --git a/module001-ch004-openstack-architecture.xml b/module001-ch004-openstack-architecture.xml
index efb262b6..6a8039b7 100644
--- a/module001-ch004-openstack-architecture.xml
+++ b/module001-ch004-openstack-architecture.xml
@@ -270,7 +270,7 @@
             limited to read-only usage.</para>
         </listitem>
       </itemizedlist>
-      <para>There are also a number of periodic process which run on
+      <para>There are also a number of periodic processes which run on
         Glance to support caching. The most important of these is the
         replication services, which ensures consistency and
         availability through the cluster. Other periodic processes