diff --git a/include/xo/randomgen/engine_concept.hpp b/include/xo/randomgen/engine_concept.hpp
index 42557b0..38b65cd 100644
--- a/include/xo/randomgen/engine_concept.hpp
+++ b/include/xo/randomgen/engine_concept.hpp
@@ -5,6 +5,37 @@
 #include <concepts>
 #include <random>
 
+namespace std {
+#ifdef __clang__
+    template < class T >
+    concept integral = std::is_integral_v<T>;
+
+    template < class T >
+    concept signed_integral = std::integral<T> && std::is_signed_v<T>;
+
+    template < class T >
+    concept unsigned_integral
+    = std::integral<T> && !std::signed_integral<T>;
+
+    template< class F, class... Args >
+    concept invocable
+    = requires(F&& f, Args&&... args) {
+        std::invoke(std::forward<F>(f), std::forward<Args>(args)...);
+        /* not required to be equality-preserving */
+    };
+
+    template< typename G >
+    concept uniform_random_bit_generator
+    = std::invocable<G&>
+        && std::unsigned_integral<std::invoke_result_t<G&>>
+        && requires { { G::min() } -> std::same_as<std::invoke_result_t<G&>>;
+                      { G::max() } -> std::same_as<std::invoke_result_t<G&>>;
+                      requires std::bool_constant<(G::min() < G::max())>::value; };
+#else
+    /* uniform_random_bit_generator provided by gcc 12.3.2 */
+#endif
+} /*namespace std*/
+
 namespace xo {
     namespace rng {
         /* an engine generates psuedo-random bits.
@@ -29,7 +60,13 @@ namespace xo {
             { engine.seed(r) };
             { engine == engine };
             { engine != engine };
-        } && std::copyable<RngEngine> && std::uniform_random_bit_generator<RngEngine>;
+        }
+#ifdef __clang__
+        // std::copyable apparently not available in clang11 ?
+#else
+            && std::copyable<RngEngine>
+#endif
+        && std::uniform_random_bit_generator<RngEngine>;
     } /*namespace rng*/
 } /*namespace xo*/
 
diff --git a/include/xo/randomgen/random_seed.hpp b/include/xo/randomgen/random_seed.hpp
index 67246c0..92447b3 100644
--- a/include/xo/randomgen/random_seed.hpp
+++ b/include/xo/randomgen/random_seed.hpp
@@ -24,7 +24,7 @@ namespace xo {
          */
         template<typename T>
         void random_seed(T * p_seed) {
-#      ifdef _BSD_SOURCE
+#      ifdef __clang__
             /* NOTE: arc4random_buf() works on darwin/nix;
              *       probably need to do something else on intel linux
              */