diff --git a/include/tao/pq/connection.hpp b/include/tao/pq/connection.hpp
index 9972046..1c67486 100644
--- a/include/tao/pq/connection.hpp
+++ b/include/tao/pq/connection.hpp
@@ -99,7 +99,7 @@ namespace tao::pq
       };
 
    public:
-      connection( const private_key /*unused*/, const std::string& connection_info, const std::function< poll::callback > poll_cb );
+      connection( const private_key /*unused*/, const std::string& connection_info, const std::function< poll::callback >& poll_cb );
 
       connection( const connection& ) = delete;
       connection( connection&& ) = delete;
@@ -108,7 +108,7 @@ namespace tao::pq
 
       ~connection() = default;
 
-      [[nodiscard]] static auto create( const std::string& connection_info, const std::function< poll::callback > poll_cb = poll::internal::default_poll ) -> std::shared_ptr< connection >;
+      [[nodiscard]] static auto create( const std::string& connection_info, const std::function< poll::callback >& poll_cb = poll::internal::default_poll ) -> std::shared_ptr< connection >;
 
       [[nodiscard]] auto error_message() const -> std::string;
 
diff --git a/include/tao/pq/connection_pool.hpp b/include/tao/pq/connection_pool.hpp
index 45ef968..beed92f 100644
--- a/include/tao/pq/connection_pool.hpp
+++ b/include/tao/pq/connection_pool.hpp
@@ -43,9 +43,9 @@ namespace tao::pq
       };
 
    public:
-      connection_pool( const private_key /*unused*/, const std::string_view connection_info, const std::function< poll::callback > poll_cb );
+      connection_pool( const private_key /*unused*/, const std::string_view connection_info, const std::function< poll::callback >& poll_cb );
 
-      [[nodiscard]] static auto create( const std::string_view connection_info, const std::function< poll::callback > poll_cb = poll::internal::default_poll ) -> std::shared_ptr< connection_pool >;
+      [[nodiscard]] static auto create( const std::string_view connection_info, const std::function< poll::callback >& poll_cb = poll::internal::default_poll ) -> std::shared_ptr< connection_pool >;
 
       [[nodiscard]] auto timeout() const noexcept -> decltype( auto )
       {
diff --git a/src/lib/pq/connection.cpp b/src/lib/pq/connection.cpp
index 9ae2655..5d4667c 100644
--- a/src/lib/pq/connection.cpp
+++ b/src/lib/pq/connection.cpp
@@ -378,7 +378,7 @@ namespace tao::pq
       }
    }
 
-   connection::connection( const private_key /*unused*/, const std::string& connection_info, const std::function< poll::callback > poll_cb )
+   connection::connection( const private_key /*unused*/, const std::string& connection_info, const std::function< poll::callback >& poll_cb )
       : m_pgconn( PQconnectdb( connection_info.c_str() ), &PQfinish ),
         m_current_transaction( nullptr ),
         m_poll( poll_cb )
@@ -394,7 +394,7 @@ namespace tao::pq
       }
    }
 
-   auto connection::create( const std::string& connection_info, const std::function< poll::callback > poll_cb ) -> std::shared_ptr< connection >
+   auto connection::create( const std::string& connection_info, const std::function< poll::callback >& poll_cb ) -> std::shared_ptr< connection >
    {
       return std::make_shared< connection >( private_key(), connection_info, poll_cb );
    }
diff --git a/src/lib/pq/connection_pool.cpp b/src/lib/pq/connection_pool.cpp
index feb7e94..89dc6f6 100644
--- a/src/lib/pq/connection_pool.cpp
+++ b/src/lib/pq/connection_pool.cpp
@@ -11,12 +11,12 @@ namespace tao::pq
       return std::make_unique< pq::connection >( pq::connection::private_key(), m_connection_info, m_poll );
    }
 
-   connection_pool::connection_pool( const private_key /*unused*/, const std::string_view connection_info, const std::function< poll::callback > poll_cb )
+   connection_pool::connection_pool( const private_key /*unused*/, const std::string_view connection_info, const std::function< poll::callback >& poll_cb )
       : m_connection_info( connection_info ),
         m_poll( poll_cb )
    {}
 
-   auto connection_pool::create( const std::string_view connection_info, const std::function< poll::callback > poll_cb ) -> std::shared_ptr< connection_pool >
+   auto connection_pool::create( const std::string_view connection_info, const std::function< poll::callback >& poll_cb ) -> std::shared_ptr< connection_pool >
    {
       return std::make_shared< connection_pool >( private_key(), connection_info, poll_cb );
    }