diff --git a/manual/viewer.rst b/manual/viewer.rst
index e17e180a33..5af7a74d1a 100644
--- a/manual/viewer.rst
+++ b/manual/viewer.rst
@@ -131,15 +131,20 @@ the username of the Content server viewer to sync with. Use the special value
 Read aloud
 ------------
 
-The viewer can read book text aloud. To use it you can simply click th
+The viewer can read book text aloud. To use it you can simply click the
 :guilabel:`Read aloud` button in the viewer controls to start reading book text
-aloud. The word being currently read is highlighted.
+aloud. The word being currently read is highlighted. Speech is synthesized from
+the text using your operating system services for text-to-speech.
 
-You can also read aloud highlighted passages by adding the read aloud button to
+You can also read aloud highlighted passages by adding the :guilabel:`Read aloud` button to
 the selection bar in the viewer preferences under :guilabel:`Selection
 behavior`.
 
 
+.. note:: On Linux, :guilabel:`Read aloud` requires `Speech Dispatcher
+   <https://freebsoft.org/speechd>`_ to be installed and working.
+
+
 Customizing the look and feel of your reading experience
 ------------------------------------------------------------