Index: trunk/psModules/src/imcombine/pmSubtraction.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtraction.c	(revision 23839)
+++ trunk/psModules/src/imcombine/pmSubtraction.c	(revision 23989)
@@ -822,4 +822,10 @@
     psFree(mask);
 
+    // XXX raise an error?
+    if (isnan(stats->sampleMean)) {
+        psFree(stats);
+        return -1;
+    }
+
     double mean, rms;                 // Mean and RMS of deviations
     if (numStamps < MIN_SAMPLE_STATS) {