diff --git a/include/boost/asio/detail/impl/win_object_handle_service.ipp b/include/boost/asio/detail/impl/win_object_handle_service.ipp
index cece0719..081d5eb4 100644
--- a/include/boost/asio/detail/impl/win_object_handle_service.ipp
+++ b/include/boost/asio/detail/impl/win_object_handle_service.ipp
@@ -421,7 +421,7 @@ void win_object_handle_service::wait_callback(PVOID param, BOOLEAN)
         boost::system::error_code ec(last_error,
             boost::asio::error::get_system_category());
 
-        while (wait_op* op = impl->op_queue_.front())
+        while ((op = impl->op_queue_.front()) != 0)
         {
           op->ec_ = ec;
           impl->op_queue_.pop();