diff --git a/PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs b/PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs
index 2d0ff7e98..89aa0dd8e 100644
--- a/PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs	
+++ b/PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs	
@@ -1011,7 +1011,7 @@ private void UpdateRandomEC(object sender, EventArgs e)
 
     private void Update255_MTB(object sender, EventArgs e)
     {
-        if (sender is not MaskedTextBox tb)
+        if (sender is not MaskedTextBox tb || !FieldsLoaded)
             return;
         if (Util.ToInt32(tb.Text) > byte.MaxValue)
             tb.Text = "255";