diff --git a/format.c b/format.c
index 92b1dd3a..96344f27 100644
--- a/format.c
+++ b/format.c
@@ -2419,20 +2419,10 @@ format_cb_pane_y(struct format_tree *ft)
 static void *
 format_cb_pane_z(struct format_tree *ft)
 {
-	struct window_pane	*wp;
-	u_int			 n = 0;
+	u_int	idx;
 
-	if (ft->wp != NULL) {
-		if (~ft->wp->flags & PANE_FLOATING)
-			return (xstrdup("0"));
-		TAILQ_FOREACH(wp, &ft->wp->window->z_index, zentry) {
-			if (wp->flags & PANE_FLOATING)
-				n++;
-			if (wp == ft->wp)
-				return (format_printf("%u", n));
-		}
-		return (xstrdup("0"));
-	}
+	if (ft->wp != NULL && window_pane_zindex(ft->wp, &idx) == 0)
+		return (format_printf("%u", idx));
 	return (NULL);
 }
 
diff --git a/sort.c b/sort.c
index a9e5da5c..fda6a90b 100644
--- a/sort.c
+++ b/sort.c
@@ -74,6 +74,7 @@ sort_buffer_cmp(const void *a0, const void *b0)
 	case SORT_INDEX:
 	case SORT_MODIFIER:
 	case SORT_ORDER:
+	case SORT_Z:
 	case SORT_END:
 		break;
 	}
@@ -120,6 +121,7 @@ sort_client_cmp(const void *a0, const void *b0)
 	case SORT_INDEX:
 	case SORT_MODIFIER:
 	case SORT_ORDER:
+	case SORT_Z:
 	case SORT_END:
 		break;
 	}
@@ -172,6 +174,7 @@ sort_session_cmp(const void *a0, const void *b0)
 	case SORT_MODIFIER:
 	case SORT_ORDER:
 	case SORT_SIZE:
+	case SORT_Z:
 	case SORT_END:
 		break;
 	}
@@ -211,6 +214,11 @@ sort_pane_cmp(const void *a0, const void *b0)
 	case SORT_NAME:
 		result = strcmp(a->screen->title, b->screen->title);
 		break;
+	case SORT_Z:
+		window_pane_zindex(a, &ai);
+		window_pane_zindex(b, &bi);
+		result = ai - bi;
+		break;
 	case SORT_MODIFIER:
 	case SORT_ORDER:
 	case SORT_END:
@@ -269,6 +277,7 @@ sort_winlink_cmp(const void *a0, const void *b0)
 		break;
 	case SORT_MODIFIER:
 	case SORT_ORDER:
+	case SORT_Z:
 	case SORT_END:
 		break;
 	}
@@ -304,6 +313,7 @@ sort_key_binding_cmp(const void *a0, const void *b0)
 	case SORT_CREATION:
 	case SORT_ORDER:
 	case SORT_SIZE:
+	case SORT_Z:
 	case SORT_END:
 		break;
 	}
@@ -358,6 +368,8 @@ sort_order_from_string(const char* order)
 			return (SORT_ORDER);
 		if (strcasecmp(order, "size") == 0)
 			return (SORT_SIZE);
+		if (strcasecmp(order, "z") == 0)
+			return (SORT_Z);
 	}
 	return (SORT_END);
 }
@@ -379,6 +391,8 @@ sort_order_to_string(enum sort_order order)
 		return "order";
 	if (order == SORT_SIZE)
 		return "size";
+	if (order == SORT_Z)
+		return "z";
 	return (NULL);
 }
 
diff --git a/tmux.1 b/tmux.1
index aaf811dd..c8c7dd41 100644
--- a/tmux.1
+++ b/tmux.1
@@ -2862,9 +2862,10 @@ is not given, "switch\-client \-t \[aq]%%\[aq]" is used.
 specifies the initial sort order: one of
 .Ql index ,
 .Ql name ,
-or
 .Ql activity
-(time).
+(time)
+or
+.Ql z .
 .Fl r
 reverses the sort order.
 .Fl f
diff --git a/tmux.h b/tmux.h
index fed51792..456c1666 100644
--- a/tmux.h
+++ b/tmux.h
@@ -2334,6 +2334,7 @@ enum sort_order {
 	SORT_NAME,
 	SORT_ORDER,
 	SORT_SIZE,
+	SORT_Z,
 	SORT_END,
 };
 
@@ -3391,6 +3392,7 @@ struct window_pane *window_pane_next_by_number(struct window *,
 struct window_pane *window_pane_previous_by_number(struct window *,
 			struct window_pane *, u_int);
 int		 window_pane_index(struct window_pane *, u_int *);
+int		 window_pane_zindex(struct window_pane *, u_int *);
 u_int		 window_count_panes(struct window *, int);
 void		 window_destroy_panes(struct window *);
 struct window_pane *window_pane_find_by_id_str(const char *);
diff --git a/window-tree.c b/window-tree.c
index 79404dd9..2f4dccd4 100644
--- a/window-tree.c
+++ b/window-tree.c
@@ -136,6 +136,7 @@ static enum sort_order window_tree_order_seq[] = {
 	SORT_INDEX,
 	SORT_NAME,
 	SORT_ACTIVITY,
+	SORT_Z,
 	SORT_END,
 };
 
diff --git a/window.c b/window.c
index 5af4f823..4b4af783 100644
--- a/window.c
+++ b/window.c
@@ -880,8 +880,8 @@ window_pane_previous_by_number(struct window *w, struct window_pane *wp,
 int
 window_pane_index(struct window_pane *wp, u_int *i)
 {
-	struct window_pane	*wq;
 	struct window		*w = wp->window;
+	struct window_pane	*wq;
 
 	*i = options_get_number(w->options, "pane-base-index");
 	TAILQ_FOREACH(wq, &w->panes, entry) {
@@ -894,6 +894,26 @@ window_pane_index(struct window_pane *wp, u_int *i)
 	return (-1);
 }
 
+int
+window_pane_zindex(struct window_pane *wp, u_int *i)
+{
+	struct window		*w = wp->window;
+	struct window_pane	*wq;
+
+	*i = 0;
+	TAILQ_FOREACH(wq, &w->z_index, zentry) {
+		if (wq == wp) {
+			if (~wp->flags & PANE_FLOATING)
+				(*i)++;
+			return (0);
+		}
+		if (wq->flags & PANE_FLOATING)
+			(*i)++;
+	}
+
+	return (-1);
+}
+
 u_int
 window_count_panes(struct window *w, int with_floating)
 {