diff --git a/asio/include/asio/co_composed.hpp b/asio/include/asio/co_composed.hpp
index 01fe29829a..f0bc98e8cc 100644
--- a/asio/include/asio/co_composed.hpp
+++ b/asio/include/asio/co_composed.hpp
@@ -845,7 +845,11 @@ class co_composed_promise
     throw;
   }
 
+#ifdef ASIO_DISABLE_CONCEPTS
+  template <typename Op>
+#else
   template <async_operation Op>
+#endif
   auto await_transform(Op&& op
 #if defined(ASIO_ENABLE_HANDLER_TRACKING)
 # if defined(ASIO_HAS_SOURCE_LOCATION)