diff --git a/cura/LayerDataDecorator.py b/cura/LayerDataDecorator.py
index 09ef54ce5e..ef82d8f5cc 100644
--- a/cura/LayerDataDecorator.py
+++ b/cura/LayerDataDecorator.py
@@ -1,9 +1,10 @@
-from typing import TYPE_CHECKING, Optional
+# Copyright (c) 2019 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
 
+from typing import Optional
 from UM.Scene.SceneNodeDecorator import SceneNodeDecorator
 
-if TYPE_CHECKING:
-    from cura.LayerData import LayerData
+from cura.LayerData import LayerData
 
 
 ## Simple decorator to indicate a scene node holds layer data.
@@ -15,10 +16,10 @@ class LayerDataDecorator(SceneNodeDecorator):
     def getLayerData(self) -> Optional["LayerData"]:
         return self._layer_data
 
-    def setLayerData(self, layer_data: Optional["LayerData"]) -> None:
+    def setLayerData(self, layer_data: LayerData) -> None:
         self._layer_data = layer_data
 
     def __deepcopy__(self, memo) -> "LayerDataDecorator":
         copied_decorator = LayerDataDecorator()
-        copied_decorator.setLayerData(self.getLayerData())
+        copied_decorator._layer_data = self._layer_data
         return copied_decorator