Index: /trunk/Ohana/src/dvomerge/src/build_links.c
===================================================================
--- /trunk/Ohana/src/dvomerge/src/build_links.c	(revision 37761)
+++ /trunk/Ohana/src/dvomerge/src/build_links.c	(revision 37762)
@@ -241,5 +241,8 @@
   for (i = 0; i < Naverage; i++) {
     if (!average[i].Nlensing) continue;
+    off_t m = average[i].lensingOffset;
+    myAssert (lensing[m].averef == i, "not sorted");
     for (j = 0; j < average[i].Nlensing - 1; j++, N++) {
+      myAssert (lensing[m+j+1].averef == i, "not sorted");
       next_lens[N] = N + 1;
       if (N >= Nlensing) {
@@ -329,5 +332,6 @@
   }
 
-  if (m == -1) {
+  // if Nlensing is 0, m may have been mis-set; add to the end
+  if ((average[0].Nlensing == 0) || (m == -1)) {
     average[0].lensingOffset = Nlensing;
   } else {