diff --git a/Ridges_3/doc/Ridges_3/Ridges_3.txt b/Ridges_3/doc/Ridges_3/Ridges_3.txt
index e060ec4d1c4..e6e30e83d92 100644
--- a/Ridges_3/doc/Ridges_3/Ridges_3.txt
+++ b/Ridges_3/doc/Ridges_3/Ridges_3.txt
@@ -44,7 +44,7 @@ functions of the package are provided in Section \ref Ridges_3Examples.
 
 For a detailed introduction to ridges and related topics, the reader
 may consult
-\cgalCite{cgal:hgygm-ttdpf-99},cgal:p-gd-01, as well as
+\cgalCite{cgal:hgygm-ttdpf-99},\cgalCite{cgal:p-gd-01}, as well as
 the following survey article \cgalCite{cgal:cp-ssulc-05}.
 In the sequel, we just introduce the basic notions so as to explain
 our algorithms. Consider a smooth embedded surface, and denote \f$ k_1\f$