diff --git a/lib/redmine/export/pdf.rb b/lib/redmine/export/pdf.rb
index 932f1a81..5918b6d3 100644
--- a/lib/redmine/export/pdf.rb
+++ b/lib/redmine/export/pdf.rb
@@ -16,6 +16,7 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
 require 'iconv'
+require 'rfpdf/fpdf'
 require 'rfpdf/chinese'
 
 module Redmine