From 4d0c43f9aa944649d4b5788c5de98d37c280a036 Mon Sep 17 00:00:00 2001
From: Jean-Marc Lasgouttes <lasgouttes@lyx.org>
Date: Fri, 1 Jun 2018 21:48:26 +0200
Subject: [PATCH] Fixup c7496a11: test emptiness before accessing elements

---
 src/Undo.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/Undo.cpp b/src/Undo.cpp
index c0cf56925e..693008268a 100644
--- a/src/Undo.cpp
+++ b/src/Undo.cpp
@@ -612,7 +612,9 @@ void Undo::endUndoGroup(CursorData const & cur_after)
 
 bool Undo::activeUndoGroup() const
 {
-	return d->group_level_ > 0 && d->undostack_.top().group_id == d->group_id_;
+	return d->group_level_ > 0
+		&& !d->undostack_.empty()
+		&& d->undostack_.top().group_id == d->group_id_;
 }
 
 
-- 
2.39.5