Index: trunk/ppSub/src/ppSubVarianceRescale.c
===================================================================
--- trunk/ppSub/src/ppSubVarianceRescale.c	(revision 27316)
+++ trunk/ppSub/src/ppSubVarianceRescale.c	(revision 27317)
@@ -54,4 +54,10 @@
     pmReadout *readout = pmFPAfileThisReadout(config->files, view, "PPSUB.OUTPUT"); // Output image
 
+    if (!readout->variance) {
+        // Nothing to renormalise
+        psWarning("Renormalisation of the variance requested, but no variance provided.");
+        return true;
+    }
+
     return pmReadoutVarianceRenormalise(readout, maskBad, num, minValid, maxValid);
 }