diff --git a/include/nbd_proxy.hpp b/include/nbd_proxy.hpp
index 17d57b4..838e7a1 100644
--- a/include/nbd_proxy.hpp
+++ b/include/nbd_proxy.hpp
@@ -125,9 +125,9 @@
 
     void send(std::string_view buffer, std::function<void()>&& onDone)
     {
-        boost::asio::buffer_copy(ws2uxBuf.prepare(buffer.size()),
-                                 boost::asio::buffer(buffer));
-        ws2uxBuf.commit(buffer.size());
+        size_t copied = boost::asio::buffer_copy(
+            ws2uxBuf.prepare(buffer.size()), boost::asio::buffer(buffer));
+        ws2uxBuf.commit(copied);
 
         doWrite(std::move(onDone));
     }