Index: trunk/ppSub/src/ppSubLoop.c
===================================================================
--- trunk/ppSub/src/ppSubLoop.c	(revision 13360)
+++ trunk/ppSub/src/ppSubLoop.c	(revision 13371)
@@ -102,10 +102,10 @@
 
             pmReadout *inRO;           // Readin of interest
-            while ((inRO = pmFPAviewNextReadout(view, input->fpa, 1)) != NULL) {
+            while ((inRO = pmFPAviewNextReadout(view, input->fpa, 1))) {
                 if (!pmFPAfileIOChecks(config, view, PM_FPA_BEFORE)) {
                     return false;
                 }
                 pmReadout *refRO = pmFPAviewThisReadout(view, reference->fpa);// Reference readout of interest
-                if ((!inRO->data_exists && refRO->data_exists) ||
+                if (!refRO || (!inRO->data_exists && refRO->data_exists) ||
                     (inRO->data_exists && !refRO->data_exists)) {
                     psError(PS_ERR_BAD_PARAMETER_VALUE, true,