diff --git a/cell.cpp b/cell.cpp
index 8e7b162f..993bcbf4 100644
--- a/cell.cpp
+++ b/cell.cpp
@@ -671,7 +671,7 @@ EX void clearfrom(heptagon *at) {
 //  if(q.size() > maxq) maxq = q.size();
     q.pop();
     DEBB(DF_MEMORY, ("from %p", at));
-    if(!at->c7) {
+    if(!at->c7 && !ls::voronoi_structure()) {
       heptagon *h = dynamic_cast<heptagon*> ((cdata_or_heptagon*) at->cdata);
       if(h) {
         if(h->alt != at) { DEBB(DF_MEMORY | DF_ERROR, ("alt error :: h->alt = ", h->alt, " expected ", at)); }