diff --git a/plugins/CuraEngineBackend/CuraEngineBackend.py b/plugins/CuraEngineBackend/CuraEngineBackend.py
index 2b3c2b29f8..b588e7d9d5 100755
--- a/plugins/CuraEngineBackend/CuraEngineBackend.py
+++ b/plugins/CuraEngineBackend/CuraEngineBackend.py
@@ -584,7 +584,7 @@ class CuraEngineBackend(QObject, Backend):
     #
     #   \param message The protobuf message containing sliced layer data.
     def _onOptimizedLayerMessage(self, message: Arcus.PythonMessage) -> None:
-        if self._start_slice_job_build_plate:
+        if self._start_slice_job_build_plate is not None:
             if self._start_slice_job_build_plate not in self._stored_optimized_layer_data:
                 self._stored_optimized_layer_data[self._start_slice_job_build_plate] = []
             self._stored_optimized_layer_data[self._start_slice_job_build_plate].append(message)