diff --git a/src/Common/src/CoreLib/System/Security/PermissionSet.cs b/src/Common/src/CoreLib/System/Security/PermissionSet.cs
index 60ef88656ed0..a9198ec92581 100644
--- a/src/Common/src/CoreLib/System/Security/PermissionSet.cs
+++ b/src/Common/src/CoreLib/System/Security/PermissionSet.cs
@@ -24,8 +24,8 @@ public PermissionSet(PermissionSet permSet) { }
         public void Assert() { }
         public bool ContainsNonCodeAccessPermissions() { return false; }
         [Obsolete]
-        public static byte[] ConvertPermissionSet(string inFormat, byte[] inData, string outFormat) { return null; }
-        public virtual PermissionSet Copy() { return default(PermissionSet); }
+        public static byte[] ConvertPermissionSet(string inFormat, byte[] inData, string outFormat) { throw new NotImplementedException(); }
+        public virtual PermissionSet Copy() { return new PermissionSet(this); }
         public virtual void CopyTo(Array array, int index) { }
         public void Demand() { }
         [Obsolete]