diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index 2adbf89b1..cce640e02 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -5598,6 +5598,7 @@ FurnaceGUI::FurnaceGUI():
 #endif
   hasACED(false),
   waveGenBaseShape(0),
+  waveInterpolation(0),
   waveGenDuty(0.5f),
   waveGenPower(1),
   waveGenInvertPoint(1.0f),