1 files changed, 1 insertions, 1 deletions
diff --git a/src/System.Private.CoreLib/shared/System/Globalization/CalendarData.Unix.cs b/src/System.Private.CoreLib/shared/System/Globalization/CalendarData.Unix.cs
index 61e06914c..c94ac0ae5 100644
--- a/src/System.Private.CoreLib/shared/System/Globalization/CalendarData.Unix.cs
+++ b/src/System.Private.CoreLib/shared/System/Globalization/CalendarData.Unix.cs
@@ -311,7 +311,7 @@ namespace System.Globalization
                         break;
                     default:
                         const string unsupportedDateFieldSymbols = "YuUrQqwWDFg";
-                        Debug.Assert(unsupportedDateFieldSymbols.IndexOf(input[index]) == -1,
+                        Debug.Assert(!unsupportedDateFieldSymbols.Contains(input[index]),
                             string.Format(CultureInfo.InvariantCulture,
                                 "Encountered an unexpected date field symbol '{0}' from ICU which has no known corresponding .NET equivalent.", 
                                 input[index]));