diff --git a/PKHeX.WinForms/Subforms/Save Editors/SAV_MailBox.cs b/PKHeX.WinForms/Subforms/Save Editors/SAV_MailBox.cs
index 9d9f2a374..bf4c03cf3 100644
--- a/PKHeX.WinForms/Subforms/Save Editors/SAV_MailBox.cs	
+++ b/PKHeX.WinForms/Subforms/Save Editors/SAV_MailBox.cs	
@@ -586,6 +586,8 @@ private void NUD_MailIDn_ValueChanged(object sender, EventArgs e)
 
     private void SwapSlots(ListBox lb, bool down)
     {
+        if (lb.SelectedIndex == -1)
+            return;
         int index = lb.SelectedIndex;
         var otherIndex = index + (down ? 1 : -1);
         if ((uint)otherIndex >= lb.Items.Count)