diff --git a/src/kiri-mode/fdm/slice.js b/src/kiri-mode/fdm/slice.js
index 9dfc5e84..2094da83 100644
--- a/src/kiri-mode/fdm/slice.js
+++ b/src/kiri-mode/fdm/slice.js
@@ -106,7 +106,8 @@ FDM.slice = function(settings, widget, onupdate, ondone) {
         solidLayers = process.sliceSolidLayers || 0,
         vaseMode = process.sliceFillType === 'vase' && !isSynth,
         metadata = widget.anno,
-        extruder = parseInt(isSynth ? process.sliceSupportNozzle : metadata.extruder || 0),
+        maxtruder = Math.max(0, device.extruders.length - 1),
+        extruder = Math.min(maxtruder, parseInt(isSynth ? process.sliceSupportNozzle : metadata.extruder || 0)),
         sliceHeight = process.sliceHeight,
         sliceHeightBase = (isBelt ? sliceHeight : process.firstSliceHeight) || sliceHeight,
         lineWidth = process.sliceLineWidth || device.extruders[extruder].extNozzle,