Index: trunk/Mars/msimreflector/MFresnelLens.cc
===================================================================
--- trunk/Mars/msimreflector/MFresnelLens.cc	(revision 19646)
+++ trunk/Mars/msimreflector/MFresnelLens.cc	(revision 19647)
@@ -699,8 +699,5 @@
         const int step = outgoing ^ !first ? 1 : -1;
         const int end  = outgoing ^ !first ? fGrooves.size() : 1;
-        const int beg  = j==0 ? ix : ix+step;
-
-        if (step==-1 && ix==1) // can not count downwards from here
-            continue;
+        const int beg  = std::max<size_t>(j==0 ? ix : ix+step, 1);
 
         for (int i=beg; i!=end; i+=step)