diff --git a/Microsoft.Toolkit.Uwp.UI/Extensions/TextBoxRegEx/TextBoxRegex.cs b/Microsoft.Toolkit.Uwp.UI/Extensions/TextBoxRegEx/TextBoxRegex.cs
index 082450754cf..e0d0cb5e277 100644
--- a/Microsoft.Toolkit.Uwp.UI/Extensions/TextBoxRegEx/TextBoxRegex.cs
+++ b/Microsoft.Toolkit.Uwp.UI/Extensions/TextBoxRegEx/TextBoxRegex.cs
@@ -105,7 +105,7 @@ private static void ValidateTextBox(TextBox textbox, bool force = true)
                     {
                         if (validationModel == ValidationMode.Dynamic)
                         {
-                            int selectionStart = textbox.SelectionStart - 1;
+                            int selectionStart = textbox.SelectionStart == 0 ? textbox.SelectionStart : textbox.SelectionStart - 1;
                             textbox.Text = textbox.Text.Remove(selectionStart, 1);
                             textbox.SelectionStart = selectionStart;
                         }