diff --git a/src/CalculatorUITestFramework/NumberPad.cs b/src/CalculatorUITestFramework/NumberPad.cs
index 225fb570..b4c7831f 100644
--- a/src/CalculatorUITestFramework/NumberPad.cs
+++ b/src/CalculatorUITestFramework/NumberPad.cs
@@ -77,7 +77,7 @@ namespace CalculatorUITestFramework
                         this.NegateButton.Click();
                         break;
                     default:
-                        throw (new ArgumentException(string.Format("{0} is not valid", digit)));
+                        throw (new ArgumentException($"{digit} is not valid"));
                 }
             }
         }