diff --git a/xs/xsp/GCode.xsp b/xs/xsp/GCode.xsp
index 12fc5d419d..6648b44537 100644
--- a/xs/xsp/GCode.xsp
+++ b/xs/xsp/GCode.xsp
@@ -11,9 +11,9 @@
         %code{% RETVAL = new CoolingBuffer(*gcode); %};
     ~CoolingBuffer();
     Ref<GCode> gcodegen();
-    void process_layer(std::string gcode, size_t layer_id)
+    std::string process_layer(std::string gcode, size_t layer_id)
         %code{%
-            THIS->process_layer(std::move(gcode), layer_id, true);
+            return THIS->process_layer(std::move(gcode), layer_id, true);
         %};
 
 };