diff --git a/package/PartSeg/common_gui/napari_image_view.py b/package/PartSeg/common_gui/napari_image_view.py
index c9fe54b9f..54dc4ab22 100644
--- a/package/PartSeg/common_gui/napari_image_view.py
+++ b/package/PartSeg/common_gui/napari_image_view.py
@@ -17,7 +17,7 @@
 from napari.utils.colormaps.colormap import ColormapInterpolationMode
 from nme import register_class
 from packaging.version import parse as parse_version
-from qtpy.QtCore import QEvent, QPoint, Qt, QTimer, Signal
+from qtpy.QtCore import QEvent, QPoint, Qt, QThread, QTimer, Signal
 from qtpy.QtWidgets import QApplication, QCheckBox, QHBoxLayout, QLabel, QMenu, QSpinBox, QToolTip, QVBoxLayout, QWidget
 from scipy.ndimage import binary_dilation
 from superqt import QEnumComboBox, ensure_main_thread
@@ -177,6 +177,8 @@ def __init__(
         self.mask_label = QLabel("Mask:")
         self.mask_label.setVisible(False)
 
+        self.prepare_layers = thread_worker(_prepare_layers)
+
         self.btn_layout = QHBoxLayout()
         self.btn_layout.addWidget(self.reset_view_button)
         self.btn_layout.addWidget(self.ndim_btn)
@@ -386,6 +388,8 @@ def update_points(self):
             self.points_layer.data = np.empty((0, 4))
 
     def set_roi(self, roi_info: Optional[ROIInfo] = None, image: Optional[Image] = None) -> None:
+        if QApplication.instance().thread() != QThread.currentThread():
+            raise RuntimeError("This method should be called from main thread")
         image = self.get_image(image)
         if roi_info is None:
             roi_info = self.settings.roi_info
@@ -601,6 +605,9 @@ def calc_filter(j, layer_):
     def _add_image(self, image_data: Tuple[ImageInfo, bool]):
         self._remove_worker(self.sender())
 
+        if QApplication.instance().thread() != QThread.currentThread():
+            raise RuntimeError("Not in main thread")
+
         image_info, replace = image_data
         image = image_info.image
         if replace:
@@ -674,7 +681,7 @@ def add_image(self, image: Optional[Image], replace=False):
         return image
 
     def _prepare_layers(self, image, parameters, replace):
-        worker = prepare_layers(image, parameters, replace)
+        worker = self.prepare_layers(image, parameters, replace)
         worker.returned.connect(self._add_image)
         self.worker_list.append(worker)
         worker.start()
diff --git a/package/PartSeg/common_gui/napari_viewer_wrap.py b/package/PartSeg/common_gui/napari_viewer_wrap.py
index c013fd0b3..5291a12d2 100644
--- a/package/PartSeg/common_gui/napari_viewer_wrap.py
+++ b/package/PartSeg/common_gui/napari_viewer_wrap.py
@@ -3,6 +3,7 @@
 
 from napari import Viewer as NViewer
 from napari.utils.colormaps import Colormap
+from qtpy.QtCore import QCoreApplication, QThread
 from qtpy.QtWidgets import QCheckBox, QFormLayout, QPushButton, QWidget
 
 from PartSeg.common_backend.base_settings import BaseSettings
@@ -244,3 +245,13 @@ def create_initial_layers(
             self._sync_widget.sync_additional()
         if points:
             self._sync_widget.sync_points()
+
+    def add_layer(self, layer):
+        if QCoreApplication.instance().thread() != QThread.currentThread():
+            raise RuntimeError("add_layer must be called from the main thread")
+        super().add_layer(layer)
+
+    def add_labels(self, *args, **kwargs):
+        if QCoreApplication.instance().thread() != QThread.currentThread():
+            raise RuntimeError("add_labels must be called from the main thread")
+        return super().add_labels(*args, **kwargs)