diff --git a/unix/gtkapp.c b/unix/gtkapp.c
index 8b2a794f..b544684e 100644
--- a/unix/gtkapp.c
+++ b/unix/gtkapp.c
@@ -196,7 +196,7 @@ void launch_duplicate_session(Conf *conf)
 {
     extern const int dup_check_launchable;
     assert(!dup_check_launchable || conf_launchable(conf));
-    new_session_window(conf, NULL);
+    new_session_window(conf_copy(conf), NULL);
 }
 
 void launch_new_session(void)