diff --git a/cellpose_napari/_dock_widget.py b/cellpose_napari/_dock_widget.py
index 87723f8..043a62f 100644
--- a/cellpose_napari/_dock_widget.py
+++ b/cellpose_napari/_dock_widget.py
@@ -279,7 +279,15 @@ def update_masks(masks):
         widget.masks_orig = masks
         logger.debug('masks updated')
 
-
+    @widget.image_layer.changed.connect
+    def check_dims(image_layer):
+        if image_layer.ndim == 4 and not image_layer.rgb:
+            widget.process_3D.value = True
+        elif image_layer.ndim==3 and not image_layer.rgb:
+            widget.process_3D.value = True
+        else:
+            widget.process_3D.value = False
+            
     @widget.compute_masks_button.changed.connect 
     def _compute_masks(e: Any):
         
diff --git a/tests/test_plugin.py b/tests/test_plugin.py
index 748f028..ff5d4e9 100644
--- a/tests/test_plugin.py
+++ b/tests/test_plugin.py
@@ -69,10 +69,13 @@ def test_compute_diameter(qtbot, viewer_widget):
 
 def test_3D_segmentation(qtbot,  viewer_widget):
     viewer, widget = viewer_widget
+    # by default the widget loads with `process_3D` set to False
+    assert widget.process_3D.value == False
     viewer.open_sample(PLUGIN_NAME, 'rgb_3D')
 
-    # set 3D processing
-    widget.process_3D.value = True
+    # check that 3D processing is set correctly after opening a 3D image
+    assert widget.process_3D.value == True
+
     widget.model_type.value = "cyto3"
     widget()  # run segmentation with all default parameters