diff --git a/src/microservices/Microservices.IdentifierMapper/Messaging/BadPatientIDException.cs b/src/microservices/Microservices.IdentifierMapper/Messaging/BadPatientIDException.cs
index ce447549c..cd0b7e55d 100644
--- a/src/microservices/Microservices.IdentifierMapper/Messaging/BadPatientIDException.cs
+++ b/src/microservices/Microservices.IdentifierMapper/Messaging/BadPatientIDException.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Runtime.Serialization;
 
 namespace Microservices.IdentifierMapper.Messaging
@@ -21,6 +21,7 @@ public BadPatientIDException(string message, Exception innerException) : base(me
         {
         }
 
+        [Obsolete("Serialising exceptions using legacy code is bad")]
         protected BadPatientIDException(SerializationInfo info, StreamingContext context) : base(info, context)
         {
         }