diff --git a/strongdef.hpp b/strongdef.hpp
index 2a0903e2..17db6329 100644
--- a/strongdef.hpp
+++ b/strongdef.hpp
@@ -31,9 +31,11 @@ namespace cruft::strongdef {
 
         constexpr explicit index (cruft::types::identity_t<T> const &_data): data (_data) { ; }
         constexpr index (index const&) = default;
+        constexpr index (index &&) = default;
 
         index& operator= (T const &) = delete;
         index& operator= (index const &) = default;
+        index& operator= (index &&) = default;
 
         // conversion operators must not be explicit or it defeats the point
         // of this class (ease of use, transparency).