diff --git a/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/NumericUpDown/Implementation/NumericUpDown.cs b/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/NumericUpDown/Implementation/NumericUpDown.cs
index 5c9d2b6b..4429a8b5 100644
--- a/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/NumericUpDown/Implementation/NumericUpDown.cs
+++ b/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/NumericUpDown/Implementation/NumericUpDown.cs
@@ -39,7 +39,8 @@ namespace Microsoft.Windows.Controls
 
         protected virtual void OnFormatStringChanged(string oldValue, string newValue)
         {
-            Text = ConvertValueToText();
+            if (IsInitialized)
+                Text = ConvertValueToText();
         }
 
         #endregion //FormatString