diff --git a/csharp/App/Backend/DataTypes/ChecklistStepDefinitions.cs b/csharp/App/Backend/DataTypes/ChecklistStepDefinitions.cs
index 3e64d2d68..71cb985bb 100644
--- a/csharp/App/Backend/DataTypes/ChecklistStepDefinitions.cs
+++ b/csharp/App/Backend/DataTypes/ChecklistStepDefinitions.cs
@@ -57,7 +57,8 @@ public static class ChecklistStepDefinitions
             """
             [
               {"text":"checklistStep10Sub1","checked":false},
-              {"text":"checklistStep10Sub2","checked":false}
+              {"text":"checklistStep10Sub2","checked":false},
+              {"text":"checklistStep10Sub3","checked":false}
             ]
             """),
         new(11, "Software verified on site",                                               NoSubtasks),
diff --git a/csharp/App/Backend/Database/Db.cs b/csharp/App/Backend/Database/Db.cs
index 4bdd7b2bb..2e3548e50 100644
--- a/csharp/App/Backend/Database/Db.cs
+++ b/csharp/App/Backend/Database/Db.cs
@@ -149,18 +149,45 @@ public static partial class Db
             "UPDATE ChecklistItem SET Subtasks = ? WHERE StepNumber = 8 AND (Subtasks IS NULL OR Subtasks = '')",
             "[{\"text\":\"checklistStep8Sub1\",\"checked\":false}]");
 
-        // One-time backfill: step 10 originally had no subtasks; add the two upload subtasks
-        // (installation protocol + time & material report) to existing rows.
+        // One-time backfill: step 10 originally had no subtasks; add the upload subtasks
+        // to existing rows.
         Connection.Execute(
             "UPDATE ChecklistItem SET Subtasks = ? WHERE StepNumber = 10 AND (Subtasks IS NULL OR Subtasks = '')",
-            "[{\"text\":\"checklistStep10Sub1\",\"checked\":false},{\"text\":\"checklistStep10Sub2\",\"checked\":false}]");
+            "[{\"text\":\"checklistStep10Sub1\",\"checked\":false},{\"text\":\"checklistStep10Sub2\",\"checked\":false},{\"text\":\"checklistStep10Sub3\",\"checked\":false}]");
+
+        // One-time backfill: append step 10 sub3 (contact Atef for external EMS) to rows
+        // that already have subtasks but lack sub3. Done in C# to handle the multi-line
+        // raw-string JSON form preserving each row's existing checked state.
+        BackfillStep10Sub3();
 
         //UpdateKeys();
         CleanupSessions().SupressAwaitWarning();
         DeleteSnapshots().SupressAwaitWarning();
     }
 
-    
+    private static void BackfillStep10Sub3()
+    {
+        var rows = Connection.Query<ChecklistItem>(
+            "SELECT * FROM ChecklistItem WHERE StepNumber = 10 AND Subtasks IS NOT NULL AND Subtasks != ''");
+        foreach (var row in rows)
+        {
+            if (row.Subtasks is null) continue;
+            if (row.Subtasks.Contains("checklistStep10Sub3")) continue;
+
+            // Insert sub3 before the closing bracket. Works regardless of indentation/whitespace
+            // since we only look for the last `]`.
+            var lastBracket = row.Subtasks.LastIndexOf(']');
+            if (lastBracket < 0) continue;
+
+            var head = row.Subtasks.Substring(0, lastBracket).TrimEnd();
+            // head ends with `}` of the last existing subtask.
+            var newJson = head + ",{\"text\":\"checklistStep10Sub3\",\"checked\":false}]";
+            Connection.Execute(
+                "UPDATE ChecklistItem SET Subtasks = ? WHERE Id = ?",
+                newJson, row.Id);
+        }
+    }
+
     private static SQLiteConnection InitConnection()
     {
         var latestDb = new DirectoryInfo("DbBackups")
diff --git a/typescript/frontend-marios2/src/lang/de.json b/typescript/frontend-marios2/src/lang/de.json
index a1b4c134a..84adaec01 100644
--- a/typescript/frontend-marios2/src/lang/de.json
+++ b/typescript/frontend-marios2/src/lang/de.json
@@ -792,6 +792,7 @@
   "checklistStep8Sub1": "Lieferschein mit Kundenunterschrift erhalten und hochgeladen",
   "checklistStep10Sub1": "Installationsprotokoll hochgeladen",
   "checklistStep10Sub2": "Zeit- und Materialbericht in Monitoring hochgeladen",
+  "checklistStep10Sub3": "Atef kontaktieren, falls externes EMS vorhanden ist",
   "checklistNoAttachments": "Noch keine Datei angehängt.",
   "setupProgress": "Setup-Fortschritt",
   "checklistPhaseEmpty": "Nicht gestartet",
diff --git a/typescript/frontend-marios2/src/lang/en.json b/typescript/frontend-marios2/src/lang/en.json
index d0a83ae9a..4c465cca0 100644
--- a/typescript/frontend-marios2/src/lang/en.json
+++ b/typescript/frontend-marios2/src/lang/en.json
@@ -540,6 +540,7 @@
   "checklistStep8Sub1": "Delivery receipt with customer signature received and uploaded",
   "checklistStep10Sub1": "Installation protocol uploaded",
   "checklistStep10Sub2": "Time and material report uploaded to Monitoring",
+  "checklistStep10Sub3": "Contact Atef if there is external EMS",
   "checklistNoAttachments": "No file attached yet.",
   "setupProgress": "Setup Progress",
   "checklistPhaseEmpty": "Not started",
diff --git a/typescript/frontend-marios2/src/lang/fr.json b/typescript/frontend-marios2/src/lang/fr.json
index 612637034..0a9d2c704 100644
--- a/typescript/frontend-marios2/src/lang/fr.json
+++ b/typescript/frontend-marios2/src/lang/fr.json
@@ -792,6 +792,7 @@
   "checklistStep8Sub1": "Bon de livraison signé par le client reçu et téléversé",
   "checklistStep10Sub1": "Procès-verbal d'installation téléversé",
   "checklistStep10Sub2": "Rapport de temps et matériaux téléversé dans Monitoring",
+  "checklistStep10Sub3": "Contacter Atef en cas d'EMS externe",
   "checklistNoAttachments": "Aucun fichier joint pour le moment.",
   "setupProgress": "Progression installation",
   "checklistPhaseEmpty": "Non commencé",
diff --git a/typescript/frontend-marios2/src/lang/it.json b/typescript/frontend-marios2/src/lang/it.json
index ed9791520..bf231f3c5 100644
--- a/typescript/frontend-marios2/src/lang/it.json
+++ b/typescript/frontend-marios2/src/lang/it.json
@@ -792,6 +792,7 @@
   "checklistStep8Sub1": "Bolla di consegna con firma del cliente ricevuta e caricata",
   "checklistStep10Sub1": "Verbale di installazione caricato",
   "checklistStep10Sub2": "Rapporto tempi e materiali caricato su Monitoring",
+  "checklistStep10Sub3": "Contattare Atef se è presente un EMS esterno",
   "checklistNoAttachments": "Nessun file allegato.",
   "setupProgress": "Avanzamento installazione",
   "checklistPhaseEmpty": "Non avviato",