diff --git a/Documentation/conf.py b/Documentation/conf.py
index 77d47bb..9eff2c8 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -273,6 +273,7 @@
     'preamble': '''
 	% Adjust margins
 	\\usepackage[margin=0.5in, top=1in, bottom=1in]{geometry}
+        \\usepackage{ifthen}
 
         % Allow generate some pages in landscape
         \\usepackage{lscape}