diff --git a/ixwebsocket/IXWebSocketTransport.cpp b/ixwebsocket/IXWebSocketTransport.cpp
index 6d901dad..47cf67ff 100644
--- a/ixwebsocket/IXWebSocketTransport.cpp
+++ b/ixwebsocket/IXWebSocketTransport.cpp
@@ -868,7 +868,7 @@ namespace ix
         }
 
         {
-            std::lock_guard<std::mutex> lock(_socketMutex);
+            std::lock_guard<std::mutex> lock(_txbufMutex);
             _txbuf.reserve(wireSize);
         }