diff --git a/src/calibre/gui2/tweak_book/boss.py b/src/calibre/gui2/tweak_book/boss.py
index c2bf95dc8b..038ab583c2 100644
--- a/src/calibre/gui2/tweak_book/boss.py
+++ b/src/calibre/gui2/tweak_book/boss.py
@@ -52,6 +52,7 @@ def setup_cssutils_serialization():
     prefs = cssutils.ser.prefs
     prefs.indent = tprefs['editor_tab_stop_width'] * ' '
     prefs.indentClosingBrace = False
+    prefs.omitLastSemicolon = False
 
 class BusyCursor(object):