diff --git a/strongdef.hpp b/strongdef.hpp
index cc02511c..0e010a4e 100644
--- a/strongdef.hpp
+++ b/strongdef.hpp
@@ -76,6 +76,18 @@ namespace cruft::strongdef {
     };
 
 
+    template <typename>
+    struct is_strongdef : public std::false_type {};
+
+
+    template <typename TagT, typename ValueT>
+    struct is_strongdef<strongdef::index<TagT, ValueT>> : public std::true_type {};
+
+
+    template <typename ValueT>
+    constexpr bool is_strongdef_v = is_strongdef<ValueT>::value;
+
+
     template <typename TagT, typename T>
     std::ostream&
     operator<< (std::ostream &os, index<TagT,T> const &val)