diff --git a/Periodic_2_triangulation_2/doc/Periodic_2_triangulation_2/Periodic_2_triangulation_2.txt b/Periodic_2_triangulation_2/doc/Periodic_2_triangulation_2/Periodic_2_triangulation_2.txt
index 1a466b34ad0..e235975dbd1 100644
--- a/Periodic_2_triangulation_2/doc/Periodic_2_triangulation_2/Periodic_2_triangulation_2.txt
+++ b/Periodic_2_triangulation_2/doc/Periodic_2_triangulation_2/Periodic_2_triangulation_2.txt
@@ -398,7 +398,7 @@ The periodic 2D-triangulation is based on the 2D triangulation package
 developed by Mariette Yvinec and inspired by the periodic 3D-triangulation package
 developed by Manuel Caroli and Monique Teillaud. The periodic
 3D-triangulation package is described in Manuel's PhD thesis 
-\cite cgal:c-tpsos-10 Triangulating Point Sets in Orbit Spaces.
+\cite cgal:c-tpsos-10 Triangulating Point Sets in Orbit Spaces and \cite cgal:ct-c3pt-09.
 
 In 2009, Nico Kruithof started implementation of the
 `Periodic_2_triangulation_2` package.