diff --git a/concepts.hpp b/concepts.hpp
index a72f99a5..243a49ad 100644
--- a/concepts.hpp
+++ b/concepts.hpp
@@ -83,7 +83,7 @@ namespace cruft::concepts {
 
 
     template <typename T>
-    concept swappable = requires (T &&a, T &&b) { swap (a, b); };
+    concept swappable = requires (T &&a, T &&b) { std::swap (a, b); };
 
 
     template < class T >
@@ -167,7 +167,7 @@ namespace cruft::concepts {
         { a.cend   () } -> same_as<typename T::const_iterator>;
 
         { a.swap (b)  } -> same_as<void>;
-        { swap (a, b) } -> same_as<void>;
+        { std::swap (a, b) } -> same_as<void>;
 
         { a.size () } -> same_as<typename T::size_type>;
         { a.max_size () } -> same_as<typename T::size_type>;