diff --git a/Envelope_3/include/CGAL/Env_sphere_traits_3.h b/Envelope_3/include/CGAL/Env_sphere_traits_3.h
index bec2a5b72a9..2a42d07f0a0 100644
--- a/Envelope_3/include/CGAL/Env_sphere_traits_3.h
+++ b/Envelope_3/include/CGAL/Env_sphere_traits_3.h
@@ -25,6 +25,8 @@
 #include <CGAL/Envelope_3/Envelope_base.h>
 #include <CGAL/int.h>
 
+#include <memory>
+
 namespace CGAL {
 
 template <typename ConicTraits_2>