diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -542,6 +542,9 @@
 	KASSERT(tp->t_fb != &tcp_def_funcblk,
 	    ("%s: called by the built-in default stack", __func__));
 
+	if (tp->t_fb->tfb_tcp_timer_stop_all != NULL)
+		tp->t_fb->tfb_tcp_timer_stop_all(tp);
+
 	/*
 	 * Now, we'll find a new function block to use.
 	 * Start by trying the current user-selected