Index: /trunk/psModules/src/imcombine/pmSubtractionStamps.c
===================================================================
--- /trunk/psModules/src/imcombine/pmSubtractionStamps.c	(revision 14518)
+++ /trunk/psModules/src/imcombine/pmSubtractionStamps.c	(revision 14519)
@@ -260,5 +260,5 @@
     if (!weight) {
         // Use the input as a rough approximation to the variance map, and HOPE that it's positive.
-        weight = input;
+        weight = input ? input : reference;
     }
 
@@ -297,5 +297,4 @@
         stamp->weight = psKernelAllocFromImage(wtSub, size, size);
         psFree(wtSub);                 // Drop reference
-
     }