diff --git a/src/gui/gui.h b/src/gui/gui.h
index 203fd20e8..45c43e56c 100644
--- a/src/gui/gui.h
+++ b/src/gui/gui.h
@@ -1611,6 +1611,7 @@ class FurnaceGUI {
 
   // wave generator
   int waveGenBaseShape;
+  int waveInterpolation;
   float waveGenDuty;
   int waveGenPower;
   float waveGenInvertPoint;