diff --git a/simple/csharp/replace-exception-with-test_after.cs b/simple/csharp/replace-exception-with-test_after.cs
index 5ec5f68..8ea0acc 100755
--- a/simple/csharp/replace-exception-with-test_after.cs
+++ b/simple/csharp/replace-exception-with-test_after.cs
@@ -1,8 +1,8 @@
 double GetValueForPeriod(int periodNumber) 
 {
-  if (periodNumber >= values.Length) 
+  if (periodNumber >= values.Length || periodNumber < 0) 
   {
     return 0;
   }
   return values[periodNumber];
-}
\ No newline at end of file
+}