diff --git a/cmd-set-option.c b/cmd-set-option.c
index 01d691d5..e236b95d 100644
--- a/cmd-set-option.c
+++ b/cmd-set-option.c
@@ -176,9 +176,7 @@ cmd_set_option_exec(struct cmd *self, struct cmd_q *cmdq)
 
 	/* Start or stop timers when automatic-rename changed. */
 	if (strcmp(oe->name, "automatic-rename") == 0) {
-		for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-			if ((w = ARRAY_ITEM(&windows, i)) == NULL)
-				continue;
+		RB_FOREACH(w, windows, &windows) {
 			if (options_get_number(&w->options, "automatic-rename"))
 				queue_window_name(w);
 			else if (event_initialized(&w->name_timer))
diff --git a/resize.c b/resize.c
index 9ad73c81..5b89b093 100644
--- a/resize.c
+++ b/resize.c
@@ -49,7 +49,7 @@ recalculate_sizes(void)
 	struct client		*c;
 	struct window		*w;
 	struct window_pane	*wp;
-	u_int			 i, j, ssx, ssy, has, limit;
+	u_int			 i, ssx, ssy, has, limit;
 	int			 flag, has_status, is_zoomed, forced;
 
 	RB_FOREACH(s, sessions, &sessions) {
@@ -57,8 +57,8 @@ recalculate_sizes(void)
 
 		s->attached = 0;
 		ssx = ssy = UINT_MAX;
-		for (j = 0; j < ARRAY_LENGTH(&clients); j++) {
-			c = ARRAY_ITEM(&clients, j);
+		for (i = 0; i < ARRAY_LENGTH(&clients); i++) {
+			c = ARRAY_ITEM(&clients, i);
 			if (c == NULL || c->flags & CLIENT_SUSPENDED)
 				continue;
 			if (c->session == s) {
@@ -92,9 +92,8 @@ recalculate_sizes(void)
 		s->sy = ssy;
 	}
 
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		w = ARRAY_ITEM(&windows, i);
-		if (w == NULL || w->active == NULL)
+	RB_FOREACH(w, windows, &windows) {
+		if (w->active == NULL)
 			continue;
 		flag = options_get_number(&w->options, "aggressive-resize");
 
diff --git a/server-client.c b/server-client.c
index c022a36f..e2f65e71 100644
--- a/server-client.c
+++ b/server-client.c
@@ -720,11 +720,7 @@ server_client_loop(void)
 	 * Any windows will have been redrawn as part of clients, so clear
 	 * their flags now. Also check pane focus and resize.
 	 */
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		w = ARRAY_ITEM(&windows, i);
-		if (w == NULL)
-			continue;
-
+	RB_FOREACH(w, windows, &windows) {
 		w->flags &= ~WINDOW_REDRAW;
 		TAILQ_FOREACH(wp, &w->panes, entry) {
 			if (wp->fd != -1) {
diff --git a/server-window.c b/server-window.c
index a2355701..f157da35 100644
--- a/server-window.c
+++ b/server-window.c
@@ -34,24 +34,20 @@ void
 server_window_loop(void)
 {
 	struct window	*w;
-	struct winlink	*wl;
 	struct session	*s;
-	u_int		 i;
-
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		w = ARRAY_ITEM(&windows, i);
-		if (w == NULL)
-			continue;
+	struct winlink	*wl;
 
+	RB_FOREACH(w, windows, &windows) {
 		RB_FOREACH(s, sessions, &sessions) {
-			wl = session_has(s, w);
-			if (wl == NULL)
-				continue;
+			RB_FOREACH(wl, winlinks, &s->windows) {
+				if (wl->window != w)
+					continue;
 
-			if (server_window_check_bell(s, wl) ||
-			    server_window_check_activity(s, wl) ||
-			    server_window_check_silence(s, wl))
-				server_status_session(s);
+				if (server_window_check_bell(s, wl) ||
+				    server_window_check_activity(s, wl) ||
+				    server_window_check_silence(s, wl))
+					server_status_session(s);
+			}
 		}
 	}
 }
diff --git a/server.c b/server.c
index bb96d9af..1183d64d 100644
--- a/server.c
+++ b/server.c
@@ -137,7 +137,7 @@ server_start(int lockfd, char *lockfile)
 	logfile("server");
 	log_debug("server started, pid %ld", (long) getpid());
 
-	ARRAY_INIT(&windows);
+	RB_INIT(&windows);
 	RB_INIT(&all_window_panes);
 	ARRAY_INIT(&clients);
 	ARRAY_INIT(&dead_clients);
@@ -438,14 +438,11 @@ server_child_signal(void)
 void
 server_child_exited(pid_t pid, int status)
 {
-	struct window		*w;
+	struct window		*w, *w1;
 	struct window_pane	*wp;
 	struct job		*job;
-	u_int		 	 i;
 
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		if ((w = ARRAY_ITEM(&windows, i)) == NULL)
-			continue;
+	RB_FOREACH_SAFE(w, windows, &windows, w1) {
 		TAILQ_FOREACH(wp, &w->panes, entry) {
 			if (wp->pid == pid) {
 				wp->status = status;
@@ -469,14 +466,11 @@ server_child_stopped(pid_t pid, int status)
 {
 	struct window		*w;
 	struct window_pane	*wp;
-	u_int			 i;
 
 	if (WSTOPSIG(status) == SIGTTIN || WSTOPSIG(status) == SIGTTOU)
 		return;
 
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		if ((w = ARRAY_ITEM(&windows, i)) == NULL)
-			continue;
+	RB_FOREACH(w, windows, &windows) {
 		TAILQ_FOREACH(wp, &w->panes, entry) {
 			if (wp->pid == pid) {
 				if (killpg(pid, SIGCONT) != 0)
@@ -493,18 +487,13 @@ server_second_callback(unused int fd, unused short events, unused void *arg)
 	struct window		*w;
 	struct window_pane	*wp;
 	struct timeval		 tv;
-	u_int		 	 i;
 
 	if (options_get_number(&global_s_options, "lock-server"))
 		server_lock_server();
 	else
 		server_lock_sessions();
 
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		w = ARRAY_ITEM(&windows, i);
-		if (w == NULL)
-			continue;
-
+	RB_FOREACH(w, windows, &windows) {
 		TAILQ_FOREACH(wp, &w->panes, entry) {
 			if (wp->mode != NULL && wp->mode->timer != NULL)
 				wp->mode->timer(wp);
diff --git a/tmux.h b/tmux.h
index 52dc1529..e52b14f1 100644
--- a/tmux.h
+++ b/tmux.h
@@ -983,8 +983,10 @@ struct window {
 	struct options	 options;
 
 	u_int		 references;
+
+	RB_ENTRY(window) entry;
 };
-ARRAY_DECL(windows, struct window *);
+RB_HEAD(windows, window);
 
 /* Entry on local window list. */
 struct winlink {
@@ -2121,6 +2123,8 @@ void	 screen_reflow(struct screen *, u_int);
 /* window.c */
 extern struct windows windows;
 extern struct window_pane_tree all_window_panes;
+int		 window_cmp(struct window *, struct window *);
+RB_PROTOTYPE(windows, window, entry, window_cmp);
 int		 winlink_cmp(struct winlink *, struct winlink *);
 RB_PROTOTYPE(winlinks, winlink, entry, winlink_cmp);
 int		 window_pane_cmp(struct window_pane *, struct window_pane *);
diff --git a/window.c b/window.c
index d8f29026..5ca8aa0c 100644
--- a/window.c
+++ b/window.c
@@ -64,6 +64,14 @@ void	window_pane_error_callback(struct bufferevent *, short, void *);
 
 struct window_pane *window_pane_choose_best(struct window_pane_list *);
 
+RB_GENERATE(windows, window, entry, window_cmp);
+
+int
+window_cmp(struct window *w1, struct window *w2)
+{
+	return (w1->id - w2->id);
+}
+
 RB_GENERATE(winlinks, winlink, entry, winlink_cmp);
 
 int
@@ -248,25 +256,18 @@ winlink_stack_remove(struct winlink_stack *stack, struct winlink *wl)
 struct window *
 window_find_by_id(u_int id)
 {
-	struct window	*w;
-	u_int		 i;
+	struct window	w;
 
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		w = ARRAY_ITEM(&windows, i);
-		if (w != NULL && w->id == id)
-			return (w);
-	}
-	return (NULL);
+	w.id = id;
+	return (RB_FIND(windows, &windows, &w));
 }
 
 struct window *
 window_create1(u_int sx, u_int sy)
 {
 	struct window	*w;
-	u_int		 i;
 
 	w = xcalloc(1, sizeof *w);
-	w->id = next_window_id++;
 	w->name = NULL;
 	w->flags = 0;
 
@@ -283,16 +284,11 @@ window_create1(u_int sx, u_int sy)
 	if (options_get_number(&w->options, "automatic-rename"))
 		queue_window_name(w);
 
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		if (ARRAY_ITEM(&windows, i) == NULL) {
-			ARRAY_SET(&windows, i, w);
-			break;
-		}
-	}
-	if (i == ARRAY_LENGTH(&windows))
-		ARRAY_ADD(&windows, w);
 	w->references = 0;
 
+	w->id = next_window_id++;
+	RB_INSERT (windows, &windows, w);
+
 	return (w);
 }
 
@@ -327,19 +323,9 @@ window_create(const char *name, int argc, char **argv, const char *path,
 void
 window_destroy(struct window *w)
 {
-	u_int	i;
-
 	window_unzoom(w);
 
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		if (w == ARRAY_ITEM(&windows, i))
-			break;
-	}
-	if (i == ARRAY_LENGTH(&windows))
-		fatalx("index not found");
-	ARRAY_SET(&windows, i, NULL);
-	while (!ARRAY_EMPTY(&windows) && ARRAY_LAST(&windows) == NULL)
-		ARRAY_TRUNC(&windows, 1);
+	RB_REMOVE(windows, &windows, w);
 
 	if (w->layout_root != NULL)
 		layout_free(w);
@@ -1328,26 +1314,18 @@ window_pane_find_right(struct window_pane *wp)
 void
 winlink_clear_flags(struct winlink *wl)
 {
-	struct winlink	*wm;
 	struct session	*s;
-	struct window	*w;
-	u_int		 i;
+	struct winlink	*wl_loop;
 
-	for (i = 0; i < ARRAY_LENGTH(&windows); i++) {
-		if ((w = ARRAY_ITEM(&windows, i)) == NULL)
-			continue;
-
-		RB_FOREACH(s, sessions, &sessions) {
-			if ((wm = session_has(s, w)) == NULL)
+	RB_FOREACH(s, sessions, &sessions) {
+		RB_FOREACH(wl_loop, winlinks, &s->windows) {
+			if (wl_loop->window != wl->window)
+				continue;
+			if ((wl_loop->flags & WINLINK_ALERTFLAGS) == 0)
 				continue;
 
-			if (wm->window != wl->window)
-				continue;
-			if ((wm->flags & WINLINK_ALERTFLAGS) == 0)
-				continue;
-
-			wm->flags &= ~WINLINK_ALERTFLAGS;
-			wm->window->flags &= ~WINDOW_ALERTFLAGS;
+			wl_loop->flags &= ~WINLINK_ALERTFLAGS;
+			wl_loop->window->flags &= ~WINDOW_ALERTFLAGS;
 			server_status_session(s);
 		}
 	}