diff --git a/Triangulation_on_sphere_2/include/CGAL/Triangulation_on_sphere_2/IO/OFF.h b/Triangulation_on_sphere_2/include/CGAL/Triangulation_on_sphere_2/IO/OFF.h
index c2868f6e636..13fc0a329ab 100644
--- a/Triangulation_on_sphere_2/include/CGAL/Triangulation_on_sphere_2/IO/OFF.h
+++ b/Triangulation_on_sphere_2/include/CGAL/Triangulation_on_sphere_2/IO/OFF.h
@@ -22,6 +22,7 @@
 
 #include <fstream>
 #include <string>
+#include <unordered_map>
 
 #ifdef DOXYGEN_RUNNING
 #define CGAL_BGL_NP_TEMPLATE_PARAMETERS NamedParameters