diff --git a/Tetrahedral_remeshing/include/CGAL/Tetrahedral_remeshing/internal/tetrahedral_remeshing_helpers.h b/Tetrahedral_remeshing/include/CGAL/Tetrahedral_remeshing/internal/tetrahedral_remeshing_helpers.h
index bc0e846fc6a..1be3eae9b0b 100644
--- a/Tetrahedral_remeshing/include/CGAL/Tetrahedral_remeshing/internal/tetrahedral_remeshing_helpers.h
+++ b/Tetrahedral_remeshing/include/CGAL/Tetrahedral_remeshing/internal/tetrahedral_remeshing_helpers.h
@@ -18,6 +18,7 @@
 #include <utility>
 #include <array>
 #include <iterator>
+#include <unordered_set>
 
 #include <CGAL/Point_3.h>
 #include <CGAL/Weighted_point_3.h>