diff --git a/format.c b/format.c
index 5c85f1ff..151c3c48 100644
--- a/format.c
+++ b/format.c
@@ -1237,17 +1237,14 @@ format_defaults_winlink(struct format_tree *ft, struct session *s,
     struct winlink *wl)
 {
 	struct window	*w = wl->window;
-	char		*flags;
 
 	if (ft->w == NULL)
 		ft->w = wl->window;
 
-	flags = window_printable_flags(s, wl);
-
 	format_defaults_window(ft, w);
 
 	format_add(ft, "window_index", "%d", wl->idx);
-	format_add(ft, "window_flags", "%s", flags);
+	format_add(ft, "window_flags", "%s", window_printable_flags(s, wl));
 	format_add(ft, "window_active", "%d", wl == s->curw);
 
 	format_add(ft, "window_bell_flag", "%d",
@@ -1259,8 +1256,6 @@ format_defaults_winlink(struct format_tree *ft, struct session *s,
 	format_add(ft, "window_last_flag", "%d",
 	    !!(wl == TAILQ_FIRST(&s->lastw)));
 	format_add(ft, "window_linked", "%d", session_is_linked(s, wl->window));
-
-	free(flags);
 }
 
 /* Set default format keys for a window pane. */
diff --git a/tmux.h b/tmux.h
index adad2edc..b8a40df0 100644
--- a/tmux.h
+++ b/tmux.h
@@ -2120,7 +2120,7 @@ int		 window_pane_outside(struct window_pane *);
 int		 window_pane_visible(struct window_pane *);
 char		*window_pane_search(struct window_pane *, const char *,
 		     u_int *);
-char		*window_printable_flags(struct session *, struct winlink *);
+const char	*window_printable_flags(struct session *, struct winlink *);
 struct window_pane *window_pane_find_up(struct window_pane *);
 struct window_pane *window_pane_find_down(struct window_pane *);
 struct window_pane *window_pane_find_left(struct window_pane *);
diff --git a/window.c b/window.c
index 0dea2b4a..b0be6220 100644
--- a/window.c
+++ b/window.c
@@ -710,11 +710,11 @@ window_destroy_panes(struct window *w)
 }
 
 /* Retuns the printable flags on a window, empty string if no flags set. */
-char *
+const char *
 window_printable_flags(struct session *s, struct winlink *wl)
 {
-	char	flags[32];
-	int	pos;
+	static char	flags[32];
+	int		pos;
 
 	pos = 0;
 	if (wl->flags & WINLINK_ACTIVITY)
@@ -732,7 +732,7 @@ window_printable_flags(struct session *s, struct winlink *wl)
 	if (wl->window->flags & WINDOW_ZOOMED)
 		flags[pos++] = 'Z';
 	flags[pos] = '\0';
-	return (xstrdup(flags));
+	return (flags);
 }
 
 struct window_pane *