Index: /trunk/ppStack/src/ppStackLoop.c
===================================================================
--- /trunk/ppStack/src/ppStackLoop.c	(revision 17641)
+++ /trunk/ppStack/src/ppStackLoop.c	(revision 17642)
@@ -445,5 +445,9 @@
 #ifndef PS_NO_TRACE
             {
-                pmReadout *ro = readouts->data[0];
+                pmReadout *ro = NULL;   // Representative readout
+                for (int i = 0; i < num && !ro; i++) {
+                    ro = readouts->data[i];
+                }
+                psAssert(ro, "There should be a readout here.");
                 psTrace("ppStack", 4, "Stack: [%d:%d,%d:%d]\n", ro->col0, ro->col0 + ro->image->numCols,
                         ro->row0, ro->row0 + ro->image->numRows);