diff --git a/features/netsocket/TCPServer.cpp b/features/netsocket/TCPServer.cpp
index 4198511f67..3ddd3b549b 100644
--- a/features/netsocket/TCPServer.cpp
+++ b/features/netsocket/TCPServer.cpp
@@ -28,6 +28,7 @@ TCPServer::~TCPServer()
 
 nsapi_error_t TCPServer::accept(TCPSocket *connection, SocketAddress *address)
 {
+    _lock.lock();
     nsapi_error_t ret;
 
     while (true) {