diff --git a/server-client.c b/server-client.c
index 2ac0eba9..1cd8f4cc 100644
--- a/server-client.c
+++ b/server-client.c
@@ -1022,7 +1022,8 @@ have_event:
 		/* Only change pane if not already dragging a pane border. */
 		if (lwp == NULL) {
 			lwp = wp = window_get_active_at(w, px, py);
-			c->tty.mouse_last_pane = wp->id;
+			if (wp != NULL)
+				c->tty.mouse_last_pane = wp->id;
 		}
 		if (c->tty.mouse_scrolling_flag == 0 &&
 		    loc == KEYC_MOUSE_LOCATION_SCROLLBAR_SLIDER) {