diff --git a/src/slic3r/GUI/DeviceCore/DevMapping.cpp b/src/slic3r/GUI/DeviceCore/DevMapping.cpp
index 5dc16f4250..165492c9f6 100644
--- a/src/slic3r/GUI/DeviceCore/DevMapping.cpp
+++ b/src/slic3r/GUI/DeviceCore/DevMapping.cpp
@@ -162,8 +162,8 @@ namespace Slic3r
                 }
 
                 //first: left,nozzle=1,map=1   second: right,nozzle=0,map=2
-                bool right_ams_valid = ams->second->GetExtruderId() == 0 && map_opt[MappingOption::USE_RIGHT_AMS];
-                bool left_ams_valid = ams->second->GetExtruderId() == 1 && map_opt[MappingOption::USE_LEFT_AMS];
+                bool right_ams_valid = (ams->second->GetBindedExtruderSet().count(MAIN_EXTRUDER_ID) != 0) && map_opt[MappingOption::USE_RIGHT_AMS];
+                bool left_ams_valid = (ams->second->GetBindedExtruderSet().count(DEPUTY_EXTRUDER_ID) != 0) && map_opt[MappingOption::USE_LEFT_AMS];
                 if (right_ams_valid || left_ams_valid)
                 {
                     tray_filaments.emplace(std::make_pair(tray_index, info));
diff --git a/tests/slic3rutils/CMakeLists.txt b/tests/slic3rutils/CMakeLists.txt
index 30f58a9562..0342450109 100644
--- a/tests/slic3rutils/CMakeLists.txt
+++ b/tests/slic3rutils/CMakeLists.txt
@@ -1,6 +1,7 @@
 get_filename_component(_TEST_NAME ${CMAKE_CURRENT_LIST_DIR} NAME)
 add_executable(${_TEST_NAME}_tests
     ${_TEST_NAME}_tests_main.cpp
+    test_dev_mapping.cpp
     )
 
 if (MSVC)
diff --git a/tests/slic3rutils/test_dev_mapping.cpp b/tests/slic3rutils/test_dev_mapping.cpp
new file mode 100644
index 0000000000..02ec2abc60
--- /dev/null
+++ b/tests/slic3rutils/test_dev_mapping.cpp
@@ -0,0 +1,81 @@
+// Match the include environment that libslic3r_gui TUs get from pchheader.hpp: Windows.h with
+// WIN32_LEAN_AND_MEAN/NOMINMAX must come first so rpcndr.h's `byte` is processed before <cstddef>
+// makes std::byte a competing candidate (otherwise the Windows COM headers pulled in via
+// DeviceManager.hpp error with an ambiguous `byte`). wx/timer.h must precede DeviceManager.hpp,
+// which includes DeviceErrorDialog.hpp (uses wxTimerEvent) before its own wx/timer.h include.
+#ifdef WIN32
+    #ifndef WIN32_LEAN_AND_MEAN
+        #define WIN32_LEAN_AND_MEAN
+    #endif
+    #ifndef NOMINMAX
+        #define NOMINMAX
+    #endif
+    #include <Windows.h>
+#endif
+
+#include <catch2/catch_all.hpp>
+
+#include <wx/timer.h>
+
+#include "slic3r/GUI/DeviceManager.hpp"
+#include "slic3r/GUI/DeviceCore/DevMapping.h"
+#include "slic3r/GUI/DeviceCore/DevFilaSystem.h"
+
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+using namespace Slic3r;
+
+TEST_CASE("Switch-bound AMS trays map to the left extruder", "[DevMapping]")
+{
+    MachineObject obj(nullptr, nullptr, "test", "test_dev", "127.0.0.1");
+
+    // aux bit 29 = Filament Track Switch installed (DevFilaSwitch.cpp:69-77)
+    obj.GetFilaSwitch()->ParseFilaSwitchInfo(json::parse(R"({"aux":"20000000"})"));
+    REQUIRE(obj.GetFilaSwitch()->IsInstalled());
+
+    // info bits: 0-3 type(1=AMS), 8-11 extruder(0xE=switch-bound), 24-27 bind_switch_in(0)
+    // tray_exist_bits bit 0 marks AMS 0 / tray 0 present so the mapping result survives the
+    // is_exists check in is_valid_mapping_result (DevFilaSystem.cpp:769).
+    // tray_info_idx/tray_type are intentionally omitted: the tray parse resolves the display
+    // filament type via MachineObject::setting_id_to_type(), which reads the GUI preset bundle
+    // (wxGetApp().preset_bundle) — unavailable in this headless unit test. The tray filament
+    // type (only needed for the type-match below) is set directly after the parse instead.
+    json print_push = json::parse(R"({
+        "ams": {
+            "tray_exist_bits": "1",
+            "ams": [ {
+                "id": "0",
+                "info": "00000E01",
+                "tray": [ { "id": "0", "tray_color": "FF0000FF" } ]
+            } ]
+        }
+    })");
+    DevFilaSystemParser::ParseV1_0(print_push, &obj, obj.GetFilaSystem().get(), false);
+
+    const auto& ams_list = obj.GetFilaSystem()->GetAmsList();
+    REQUIRE(ams_list.count("0") == 1);
+    REQUIRE(ams_list.at("0")->GetBindedExtruderSet().count(MAIN_EXTRUDER_ID) == 1);
+    REQUIRE(ams_list.at("0")->GetBindedExtruderSet().count(DEPUTY_EXTRUDER_ID) == 1);
+
+    DevAmsTray* tray = obj.GetFilaSystem()->GetAmsTray("0", "0");
+    REQUIRE(tray != nullptr);
+    tray->m_fila_type = "PLA";
+
+    FilamentInfo fila;
+    fila.id    = 0;
+    fila.type  = "PLA";
+    fila.color = "FF0000FF";
+
+    std::vector<FilamentInfo> result;
+    std::vector<bool> map_opt(4, false);       // MappingOption: LEFT_AMS,RIGHT_AMS,LEFT_EXT,RIGHT_EXT (DevMapping.h:13-19)
+    map_opt[MappingOption::USE_LEFT_AMS] = true;
+
+    DevMappingUtil::ams_filament_mapping(&obj, {fila}, result, map_opt, {}, false);
+
+    // A switch-bound AMS feeds BOTH extruders, so a left-only mapping request
+    // must still land the filament on the AMS tray.
+    REQUIRE(result.size() == 1);
+    CHECK(result[0].tray_id == 0);
+    CHECK(result[0].ams_id == "0");
+}