diff --git a/DigitalLearningSolutions.Data.Migrations/202412020900_UpdateCandidateAssessmentSupervisorsTable.cs b/DigitalLearningSolutions.Data.Migrations/202412020900_UpdateCandidateAssessmentSupervisorsTable.cs
new file mode 100644
index 0000000000..0304c7aade
--- /dev/null
+++ b/DigitalLearningSolutions.Data.Migrations/202412020900_UpdateCandidateAssessmentSupervisorsTable.cs
@@ -0,0 +1,36 @@
+namespace DigitalLearningSolutions.Data.Migrations
+{
+    using FluentMigrator;
+
+    [Migration(202412020900)]
+    public class UpdateCandidateAssessmentSupervisorsTable : ForwardOnlyMigration
+    {
+        public override void Up()
+        {
+            Execute.Sql($@"UPDATE cas 
+                SET SelfAssessmentSupervisorRoleID = (SELECT ID FROM SelfAssessmentSupervisorRoles 
+								        WHERE SelfAssessmentID = ssr.SelfAssessmentID and AllowDelegateNomination = 1) 
+                FROM CandidateAssessmentSupervisors cas INNER JOIN 
+                    SelfAssessmentSupervisorRoles ssr ON cas.SelfAssessmentSupervisorRoleID = ssr.ID 
+                    AND cas.Removed IS NULL AND ssr.AllowDelegateNomination = 0 INNER JOIN 
+                    SupervisorDelegates sd ON cas.SupervisorDelegateId = sd.ID INNER JOIN 
+                    AdminAccounts aa ON sd.SupervisorAdminID = aa.ID 
+		        WHERE aa.IsSupervisor = 0 AND aa.IsNominatedSupervisor = 1
+				        -- to exclude duplicate CandidateAssessmentID from update
+				        AND cas.CandidateAssessmentID NOT IN (
+					        SELECT CandidateAssessmentID FROM CandidateAssessmentSupervisors WHERE CandidateAssessmentID in (
+						        SELECT Cas2.CandidateAssessmentID
+						        FROM CandidateAssessmentSupervisors cas2 with (nolock) INNER JOIN 
+							        SelfAssessmentSupervisorRoles ssr2 with (nolock) ON cas2.SelfAssessmentSupervisorRoleID = ssr2.ID 
+							        AND cas2.Removed IS NULL AND ssr2.AllowDelegateNomination = 0 INNER JOIN
+							        SupervisorDelegates sd2 with (nolock) ON cas2.SupervisorDelegateId = sd2.ID INNER JOIN
+							        AdminAccounts aa2 with (nolock) ON sd2.SupervisorAdminID = aa2.ID
+						        WHERE aa2.IsSupervisor = 0 AND aa2.IsNominatedSupervisor = 1
+					        )
+					        GROUP BY CandidateAssessmentID,SupervisorDelegateId
+					        HAVING COUNT(*)>1
+					        )"
+            );
+        }
+    }
+}
diff --git a/DigitalLearningSolutions.Data/DataServices/CourseDataService.cs b/DigitalLearningSolutions.Data/DataServices/CourseDataService.cs
index 9f0ab58aec..9e3addf30f 100644
--- a/DigitalLearningSolutions.Data/DataServices/CourseDataService.cs
+++ b/DigitalLearningSolutions.Data/DataServices/CourseDataService.cs
@@ -542,7 +542,7 @@ LEFT OUTER JOIN UserCentreDetails AS UCD ON
                         new { candidateAssessmentId, enrolmentMethodId, completeByDateDynamic }
                     );
             }
-            if (candidateAssessmentId > 1 && supervisorDelegateId !=0)
+            if (candidateAssessmentId > 1 && supervisorDelegateId != 0)
             {
                 string sqlQuery = $@"
                 BEGIN TRANSACTION
@@ -551,17 +551,17 @@ BEGIN TRANSACTION
 
                 UPDATE CandidateAssessmentSupervisors SET Removed = NULL
                  {((selfAssessmentSupervisorRoleId > 0) ? " ,SelfAssessmentSupervisorRoleID = @selfAssessmentSupervisorRoleID" : string.Empty)}
-                WHERE CandidateAssessmentID = @candidateAssessmentId
+                WHERE CandidateAssessmentID = @candidateAssessmentId AND SupervisorDelegateId = @supervisorDelegateId 
 
                 COMMIT TRANSACTION";
 
                 connection.Execute(sqlQuery
-                , new { candidateAssessmentId, selfAssessmentSupervisorRoleId, enrolmentMethodId, completeByDateDynamic });
+                , new { candidateAssessmentId, selfAssessmentSupervisorRoleId, enrolmentMethodId, completeByDateDynamic, supervisorDelegateId });
             }
 
             if (supervisorId > 0)
             {
-                
+
                 var adminUserId = Convert.ToInt32(connection.ExecuteScalar(@"SELECT UserID FROM AdminAccounts WHERE (AdminAccounts.ID = @supervisorId)",
                     new { supervisorId })
                     );