diff --git a/cast.hpp b/cast.hpp
index 37e6d58b..ed4fbb98 100644
--- a/cast.hpp
+++ b/cast.hpp
@@ -8,6 +8,8 @@
 
 #pragma once
 
+
+#include "concepts.hpp"
 #include "debug/assert.hpp"
 #include "debug/validate.hpp"
 #include "platform.hpp"
@@ -72,17 +74,13 @@ namespace cruft::cast {
     /// Identity casts are allowed so as to simplify the use of this routine
     /// in template code.
     template <
-        typename NarrowT,
-        typename WideT,
-        typename = std::enable_if_t<
-            std::is_arithmetic_v<NarrowT> &&
-            std::is_arithmetic_v<WideT> &&
-            std::is_signed_v<NarrowT> == std::is_signed_v<WideT> &&
-            std::is_floating_point_v<NarrowT> == std::is_floating_point_v<WideT> &&
-            sizeof (NarrowT) <= sizeof (WideT),
-            void
-        >
+        concepts::arithmetic NarrowT,
+        concepts::arithmetic WideT
     >
+    requires
+        (std::is_signed_v<NarrowT> == std::is_signed_v<WideT>) &&
+        (std::is_floating_point_v<NarrowT> == std::is_floating_point_v<WideT>) &&
+        (sizeof (NarrowT) <= sizeof (WideT))
     constexpr NarrowT
     narrow (const WideT &val)
     {