diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Model/FormatTest.cs b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Model/FormatTest.cs
index ddf16ddad53..2bf7d5997d2 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Model/FormatTest.cs
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Model/FormatTest.cs
@@ -415,7 +415,7 @@ namespace IO.Swagger.Model
             Regex regex_String = new Regex(@"[a-z]", RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);
             if (false == regex_String.Match(this._String).Success)
             {
-                yield return new System.ComponentModel.DataAnnotations.ValidationResult("Invalid value for _String, must match a pattern of " + regex_String, new [] { "_String" });
+                yield return new System.ComponentModel.DataAnnotations.ValidationResult("Invalid value for _String, must match a pattern of /[a-z]/i.", new [] { "_String" });
             }
 
             // _Byte (byte[]) pattern
diff --git a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Model/FormatTest.cs b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Model/FormatTest.cs
index 706354c7b2d..8762cbe9751 100644
--- a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Model/FormatTest.cs
+++ b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Model/FormatTest.cs
@@ -438,7 +438,7 @@ namespace IO.Swagger.Model
             Regex regex_String = new Regex(@"[a-z]", RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);
             if (false == regex_String.Match(this._String).Success)
             {
-                yield return new System.ComponentModel.DataAnnotations.ValidationResult("Invalid value for _String, must match a pattern of " + regex_String, new [] { "_String" });
+                yield return new System.ComponentModel.DataAnnotations.ValidationResult("Invalid value for _String, must match a pattern of /[a-z]/i.", new [] { "_String" });
             }
 
             // _Byte (byte[]) pattern