diff --git a/format.c b/format.c
index 60067e4c..115eba94 100644
--- a/format.c
+++ b/format.c
@@ -1393,6 +1393,7 @@ format_defaults_pane(struct format_tree *ft, struct window_pane *wp)
 	format_add(ft, "pane_id", "%%%u", wp->id);
 	format_add(ft, "pane_active", "%d", wp == wp->window->active);
 	format_add(ft, "pane_input_off", "%d", !!(wp->flags & PANE_INPUTOFF));
+	format_add(ft, "pane_pipe", "%d", wp->pipe_fd != -1);
 
 	status = wp->status;
 	if (wp->fd == -1 && WIFEXITED(status))
diff --git a/tmux.1 b/tmux.1
index 494f231b..4f9e3e5d 100644
--- a/tmux.1
+++ b/tmux.1
@@ -3596,6 +3596,7 @@ The following variables are available, where appropriate:
 .It Li "pane_left" Ta "" Ta "Left of pane"
 .It Li "pane_mode" Ta "" Ta "Name of pane mode, if any."
 .It Li "pane_pid" Ta "" Ta "PID of first process in pane"
+.It Li "pane_pipe" Ta "" Ta "1 if pane is being piped"
 .It Li "pane_right" Ta "" Ta "Right of pane"
 .It Li "pane_search_string" Ta "" Ta "Last search string in copy mode"
 .It Li "pane_start_command" Ta "" Ta "Command pane started with"