Index: /trunk/psphot/src/psphotSubtractBackground.c
===================================================================
--- /trunk/psphot/src/psphotSubtractBackground.c	(revision 38310)
+++ /trunk/psphot/src/psphotSubtractBackground.c	(revision 38311)
@@ -64,5 +64,5 @@
     // back-sub image pixels, from output background file (don't create if not requested)
     // XXX for now, we will only allow a single background-subtracted image to be generated
-    file = psMetadataLookupPtr (&status, config->files, "PSPHOT.BACKSUB");
+    file = psMetadataLookupPtr (&status, config->files, psphotGetFilerule("PSPHOT.BACKSUB"));
     if (file) {
         // we are using PSPHOT.BACKSUB as an I/O file: select readout or create