diff --git a/include/net/tcp.h b/include/net/tcp.h
index d1dcb596230e87765e79d8cc9767da123cd69a27..4475aaf0af577cd5c778f65c4348380c6219742e 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -282,7 +282,6 @@ extern int sysctl_tcp_base_mss;
 extern int sysctl_tcp_workaround_signed_windows;
 extern int sysctl_tcp_slow_start_after_idle;
 extern int sysctl_tcp_max_ssthresh;
-extern int sysctl_tcp_cookie_size;
 extern int sysctl_tcp_thin_linear_timeouts;
 extern int sysctl_tcp_thin_dupack;
 extern int sysctl_tcp_early_retrans;