diff --git a/Source/TcpPort.m b/Source/TcpPort.m
index 1111eab0c..c0d21db1d 100644
--- a/Source/TcpPort.m
+++ b/Source/TcpPort.m
@@ -48,6 +48,7 @@
 #include <Foundation/NSMapTable.h>
 #include <Foundation/NSPortMessage.h>
 #include <Foundation/NSPortNameServer.h>
+#include <Foundation/NSLock.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <signal.h>