diff --git a/src/slic3r/GUI/DeviceCore/DevFilaSystem.cpp b/src/slic3r/GUI/DeviceCore/DevFilaSystem.cpp
index bef0391109..0e8b1ea12b 100644
--- a/src/slic3r/GUI/DeviceCore/DevFilaSystem.cpp
+++ b/src/slic3r/GUI/DeviceCore/DevFilaSystem.cpp
@@ -995,16 +995,22 @@ void DevFilaSystemParser::ParseAgentFilament(const json& data, MachineObject* ob
     }
 
     // --- external / direct spools -> obj->vt_slot ---
-    // extruder 0 -> main virtual slot, extruder >0 -> deputy.
+    // Keep one virtual slot per extruder. The legacy two-extruder mapping uses
+    // 255 for extruder 0 and 254 for extruder 1; continue that sequence for
+    // additional extruders (253, 252, ...).
     if (obj && data.contains("external") && data["external"].is_array())
     {
+        std::map<int, DevAmsTray> external_slots;
         obj->vt_slot.clear();
         for (const auto& e : data["external"])
         {
             if (!e.is_object())
                 continue;
             const int  ext   = e.value("extruder", MAIN_EXTRUDER_ID);
-            const int  vt_id = (ext == MAIN_EXTRUDER_ID) ? VIRTUAL_TRAY_MAIN_ID : VIRTUAL_TRAY_DEPUTY_ID;
+            if (ext < MAIN_EXTRUDER_ID || ext > VIRTUAL_TRAY_MAIN_ID)
+                continue;
+
+            const int  vt_id = VIRTUAL_TRAY_MAIN_ID - ext;
             DevAmsTray tray(std::to_string(vt_id));
             tray.is_exists       = e.value("loaded", false);
             tray.m_fila_type     = e.value("material", std::string());
@@ -1013,8 +1019,11 @@ void DevFilaSystemParser::ParseAgentFilament(const json& data, MachineObject* ob
             tray.nozzle_temp_min = std::to_string(e.value("nozzle_temp_min", 0));
             tray.nozzle_temp_max = std::to_string(e.value("nozzle_temp_max", 0));
             tray.remain          = e.value("remain_percent", -1);
-            obj->vt_slot.push_back(tray);
+            external_slots.insert_or_assign(ext, std::move(tray));
         }
+
+        for (auto& entry : external_slots)
+            obj->vt_slot.push_back(std::move(entry.second));
     }
 }
 
diff --git a/tests/slic3rutils/test_dev_mapping.cpp b/tests/slic3rutils/test_dev_mapping.cpp
index 4e32bcc20d..ce4727d68f 100644
--- a/tests/slic3rutils/test_dev_mapping.cpp
+++ b/tests/slic3rutils/test_dev_mapping.cpp
@@ -63,6 +63,32 @@ TEST_CASE("AMS tray placeholder state follows the latest status", "[DevFilaSyste
     CHECK_FALSE(tray->is_slot_placeholder);
 }
 
+TEST_CASE("Agent external filament slots preserve every extruder", "[DevFilaSystem]")
+{
+    MachineObject obj(nullptr, nullptr, "test", "test_dev", "127.0.0.1");
+
+    const json filament = json::parse(R"({
+        "external": [
+            { "extruder": 3, "loaded": true, "material": "PETG", "preset_id": "P3" },
+            { "extruder": 0, "loaded": true, "material": "PLA",  "preset_id": "P0" },
+            { "extruder": 2, "loaded": false, "material": "ABS", "preset_id": "P2" },
+            { "extruder": 1, "loaded": true, "material": "ASA",  "preset_id": "P1" }
+        ]
+    })");
+
+    DevFilaSystemParser::ParseAgentFilament(filament, &obj, obj.GetFilaSystem().get());
+
+    REQUIRE(obj.vt_slot.size() == 4);
+    CHECK(obj.vt_slot[0].id == "255");
+    CHECK(obj.vt_slot[1].id == "254");
+    CHECK(obj.vt_slot[2].id == "253");
+    CHECK(obj.vt_slot[3].id == "252");
+    CHECK(obj.vt_slot[0].setting_id == "P0");
+    CHECK(obj.vt_slot[1].setting_id == "P1");
+    CHECK(obj.vt_slot[2].setting_id == "P2");
+    CHECK(obj.vt_slot[3].setting_id == "P3");
+}
+
 TEST_CASE("Switch-bound AMS trays map to the left extruder", "[DevMapping]")
 {
     MachineObject obj(nullptr, nullptr, "test", "test_dev", "127.0.0.1");