diff --git a/Shape_detection/include/CGAL/Shape_detection/Region_growing/Region_growing.h b/Shape_detection/include/CGAL/Shape_detection/Region_growing/Region_growing.h
index 77b72e675ac..9c4f52ecdde 100644
--- a/Shape_detection/include/CGAL/Shape_detection/Region_growing/Region_growing.h
+++ b/Shape_detection/include/CGAL/Shape_detection/Region_growing/Region_growing.h
@@ -20,6 +20,9 @@
 #include <queue>
 #include <vector>
 
+// Boost includes.
+#include <boost/unordered_map.hpp>
+
 // CGAL includes.
 #include <CGAL/assertions.h>
 #include <CGAL/is_iterator.h>