diff --git a/src/gui/doAction.cpp b/src/gui/doAction.cpp
index 168acee83..29bc08bd2 100644
--- a/src/gui/doAction.cpp
+++ b/src/gui/doAction.cpp
@@ -772,9 +772,19 @@ void FurnaceGUI::doAction(int what) {
 
     
     case GUI_ACTION_WAVE_LIST_ADD: {
+      std::vector<DivSystem> alreadyDone;
       waveSizeList.clear();
       for (int i=0; i<e->song.systemLen; i++) {
+        bool skip=false;
+        for (DivSystem j: alreadyDone) {
+          if (e->song.system[i]==j) {
+            skip=true;
+            break;
+          }
+        }
+        if (skip) continue;
         const DivSysDef* sysDef=e->getSystemDef(e->song.system[i]);
+        alreadyDone.push_back(e->song.system[i]);
         if (sysDef==NULL) continue;
 
         if (sysDef->waveHeight==0) continue;