Index: trunk/psastro/src/psastroLoadRefstars.c
===================================================================
--- trunk/psastro/src/psastroLoadRefstars.c	(revision 34301)
+++ trunk/psastro/src/psastroLoadRefstars.c	(revision 34966)
@@ -363,4 +363,7 @@
     if (!status) ESCAPE ("missing DVO.GETSTAR.MIN.MAG.INST");
 
+    // if non zero override the zero point for the photcode (for stacks)
+    float fixedzeropt = psMetadataLookupF32(&status, recipe, "DVO.GETSTAR.FIXED.ZEROPT");
+
     // PHOTCODE.DATA is a multi of metadata items
     psListIterator *iter = psListIteratorAlloc(item->data.list, PS_LIST_HEAD, false);
@@ -391,4 +394,8 @@
             continue;
         }
+        if (fixedzeropt != 0.0) {
+            // override the recipe's zero point with the fixed value (for stacks)
+            zeropt = fixedzeropt;
+        }
 
         // convert the minInst to a calibrated minimum magnitude