diff --git a/xs/xsp/GCode.xsp b/xs/xsp/GCode.xsp
index 6648b44537..78a5dde376 100644
--- a/xs/xsp/GCode.xsp
+++ b/xs/xsp/GCode.xsp
@@ -12,9 +12,7 @@
     ~CoolingBuffer();
     Ref<GCode> gcodegen();
     std::string process_layer(std::string gcode, size_t layer_id)
-        %code{%
-            return THIS->process_layer(std::move(gcode), layer_id, true);
-        %};
+        %code{% RETVAL = THIS->process_layer(std::move(gcode), layer_id, true); %};
 
 };