Index: /trunk/psphot/src/psphotApResid.c
===================================================================
--- /trunk/psphot/src/psphotApResid.c	(revision 17109)
+++ /trunk/psphot/src/psphotApResid.c	(revision 17110)
@@ -14,5 +14,4 @@
 
     PS_ASSERT_PTR_NON_NULL(psf, false);
-    // XXX drop this? PS_ASSERT_PTR_NON_NULL(psf->ApTrend, false);
     PS_ASSERT_PTR_NON_NULL(readout, false);
     PS_ASSERT_PTR_NON_NULL(sources, false);
@@ -20,4 +19,9 @@
 
     psTimerStart ("psphot");
+
+    bool measureAptrend = psMetadataLookupBool (&status, recipe, "MEASURE.APTREND");
+    if (!measureAptrend) {
+      return true;
+    }
 
     // user-defined masks to test for good/bad pixels (build from recipe list if not yet set)