diff --git a/plugins/CuraEngineBackend/StartSliceJob.py b/plugins/CuraEngineBackend/StartSliceJob.py
index 43d54d8b12..d30a77177f 100644
--- a/plugins/CuraEngineBackend/StartSliceJob.py
+++ b/plugins/CuraEngineBackend/StartSliceJob.py
@@ -153,7 +153,7 @@ class StartSliceJob(Job):
             self.setResult(StartJobResult.MaterialIncompatible)
             return
 
-        for position, extruder_stack in stack.extruders.items():
+        for extruder_stack in stack.extruderList:
             material = extruder_stack.findContainer({"type": "material"})
             if not extruder_stack.isEnabled:
                 continue
@@ -162,7 +162,6 @@ class StartSliceJob(Job):
                     self.setResult(StartJobResult.MaterialIncompatible)
                     return
 
-
         # Don't slice if there is a per object setting with an error value.
         for node in DepthFirstIterator(self._scene.getRoot()):
             if not isinstance(node, CuraSceneNode) or not node.isSelectable():