diff --git a/manual/viewer.rst b/manual/viewer.rst
index 3dce85af6e..b895de5d2c 100644
--- a/manual/viewer.rst
+++ b/manual/viewer.rst
@@ -91,7 +91,7 @@ These buttons behave just like those in a web browser.
 Reference mode
 ^^^^^^^^^^^^^^^^^
 
-calibre also has a very handy :guilabel:`Reference mode`.  You can turn it on
+calibre also has a very handy :guilabel:`Reference mode`. You can turn it on
 by clicking the :guilabel:`Reference mode` button in the viewer controls.  Once
 you do this, every paragraph will have a unique number displayed at the start,
 made up of the section and paragraph numbers.