From d5224d4bb0a98f55c1da1cae9eaab6a57d4b3697 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Tue, 6 Oct 2020 11:43:56 +0200
Subject: [PATCH] Ensure valid index before calculating offset.

---
 src/Avalonia.Layout/StackLayout.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Avalonia.Layout/StackLayout.cs b/src/Avalonia.Layout/StackLayout.cs
index 909c7bc7eb..4a93c8344f 100644
--- a/src/Avalonia.Layout/StackLayout.cs
+++ b/src/Avalonia.Layout/StackLayout.cs
@@ -249,8 +249,8 @@ namespace Avalonia.Layout
                     realizationWindowOffsetInExtent + _orientation.MajorSize(realizationRect) >= 0 && realizationWindowOffsetInExtent <= majorSize)
                 {
                     anchorIndex = (int) (realizationWindowOffsetInExtent / averageElementSize);
-                    offset = anchorIndex* averageElementSize + _orientation.MajorStart(lastExtent);
                     anchorIndex = Math.Max(0, Math.Min(itemsCount - 1, anchorIndex));
+                    offset = anchorIndex* averageElementSize + _orientation.MajorStart(lastExtent);
                 }
         }