diff --git a/rogueviz/kohonen.cpp b/rogueviz/kohonen.cpp
index a24238d5..74c84d57 100644
--- a/rogueviz/kohonen.cpp
+++ b/rogueviz/kohonen.cpp
@@ -969,7 +969,7 @@ namespace levelline {
     if(levellines.size() == 0) create();
     on = false;
     for(auto& lv: levellines) {
-      if(!lv.qty) { lv.values.clear(); continue; }
+      if(!lv.qty || lv.qty < 0) { lv.values.clear(); continue; }
       on = true;
       if(!lv.modified) continue;
       lv.modified = false;