Index: /trunk/psModules/src/imcombine/pmSubtractionMatch.c
===================================================================
--- /trunk/psModules/src/imcombine/pmSubtractionMatch.c	(revision 18201)
+++ /trunk/psModules/src/imcombine/pmSubtractionMatch.c	(revision 18202)
@@ -95,6 +95,8 @@
                                  )
 {
-    varFactor *= (region->x1 - region->x1 + 1) * (region->y1 * region->y1 + 1) /
-        (ro->image->numCols * ro->image->numRows);
+    if (region) {
+        varFactor *= (region->x1 - region->x1 + 1) * (region->y1 * region->y1 + 1) /
+            (ro->image->numCols * ro->image->numRows);
+    }
 
     psMetadataItem *vfItem = psMetadataLookup(ro->analysis, PM_SUBTRACTION_ANALYSIS_VARFACTOR);