diff --git a/parse/enum.hpp b/parse/enum.hpp
index f0aea983..77d4e08a 100644
--- a/parse/enum.hpp
+++ b/parse/enum.hpp
@@ -18,6 +18,25 @@
 
 namespace cruft::parse::enumeration {
     namespace detail {
+        /// Map a type to the underlying enum type if it is an enum, else
+        /// provided the identity mapping. Useful so simplify template logic
+        /// when dealing with types that aren't quite enums proper.
+        template <typename EnumT, typename = void>
+        struct underlying_else_identity { using type = EnumT; };
+
+
+        // Specialise for the enum case.
+        template <typename EnumT>
+        struct underlying_else_identity<
+            EnumT,
+            std::enable_if_t<std::is_enum_v<EnumT>>
+        > { using type = std::underlying_type_t<EnumT>; };
+
+
+        template <typename EnumT>
+        using underlying_else_identity_t = typename underlying_else_identity<EnumT>::type;
+
+
         /// Abstract base class for lookups from string names to typed
         /// integers.
         ///
@@ -45,9 +64,7 @@ namespace cruft::parse::enumeration {
         /// specialised on the EnumT that the lookup is targetting.
         template <typename EnumT>
         struct lookup_concrete : public lookup_base {
-            static_assert (std::is_enum_v<EnumT>);
-
-            using underlying_type = std::underlying_type_t<EnumT>;
+            using underlying_type = underlying_else_identity_t<EnumT>;
             using cache_type = std::map<std::string_view, EnumT>;
 
             lookup_concrete (cache_type _cache)
@@ -101,21 +118,6 @@ namespace cruft::parse::enumeration {
             std::unique_ptr<lookup_base>
         >&
         cache (void);
-
-
-        /// Map a type to the underlying enum type if it is an enum, else
-        /// provided the identity mapping. Useful so simplify template logic
-        /// when dealing with types that aren't quite enums proper.
-        template <typename EnumT, typename = void>
-        struct underlying_else_identity { using type = EnumT; };
-
-
-        // Specialise for the enum case.
-        template <typename EnumT>
-        struct underlying_else_identity<
-            EnumT,
-            std::enable_if_t<std::is_enum_v<EnumT>>
-        > { using type = std::underlying_type_t<EnumT>; };
     };
 
 
@@ -165,7 +167,7 @@ namespace cruft::parse::enumeration {
             sizeof (EnumT) == 8
         );
 
-        using underlying_type = typename detail::underlying_else_identity<EnumT>::type;
+        using underlying_type = detail::underlying_else_identity_t<EnumT>;
         static_assert (std::is_integral_v<underlying_type>);
 
         if constexpr (std::is_signed_v<underlying_type>) {