diff --git a/docs/getting_started/docs-build.rst b/docs/getting_started/docs-build.rst
index fa07642..c5625e9 100644
--- a/docs/getting_started/docs-build.rst
+++ b/docs/getting_started/docs-build.rst
@@ -22,6 +22,9 @@
 - Python 3 (3.5 or later)
 - PlantUML (1.2017.15 or later)
 
+Optionally, the `Dia`_ application can be installed if you need to edit
+existing ``.dia`` diagram files, or create new ones.
+
 You must also install the Python modules that are specified in the
 ``requirements.txt`` file in the root of the ``docs`` directory. These modules
 can be installed using ``pip3`` (the Python Package Installer). Passing this
@@ -33,7 +36,7 @@
 
 .. code:: shell
 
-    sudo apt install python3 python3-pip plantuml
+    sudo apt install python3 python3-pip plantuml [dia]
     pip3 install [--user] -r requirements.txt
 
 .. note::
@@ -75,3 +78,4 @@
 
 .. _Sphinx: http://www.sphinx-doc.org/en/master/
 .. _pip homepage: https://pip.pypa.io/en/stable/
+.. _Dia: https://wiki.gnome.org/Apps/Dia