diff --git a/include/boost/asio/detail/service_registry.hpp b/include/boost/asio/detail/service_registry.hpp
index 85cde13b..ac954854 100644
--- a/include/boost/asio/detail/service_registry.hpp
+++ b/include/boost/asio/detail/service_registry.hpp
@@ -167,7 +167,8 @@ private:
   }
 
   // Check if a service matches the given id.
-  bool service_id_matches(const boost::asio::io_service::service& service,
+  static bool service_id_matches(
+      const boost::asio::io_service::service& service,
       const boost::asio::io_service::id& id)
   {
     return service.id_ == &id;
@@ -175,7 +176,8 @@ private:
 
   // Check if a service matches the given id.
   template <typename Service>
-  bool service_id_matches(const boost::asio::io_service::service& service,
+  static bool service_id_matches(
+      const boost::asio::io_service::service& service,
       const boost::asio::detail::service_id<Service>& /*id*/)
   {
     return service.type_info_ != 0 && *service.type_info_ == typeid(Service);