Index: trunk/psphot/src/psphotSersicModelClass.c
===================================================================
--- trunk/psphot/src/psphotSersicModelClass.c	(revision 33409)
+++ trunk/psphot/src/psphotSersicModelClass.c	(revision 33410)
@@ -546,4 +546,8 @@
     // set the normalization by linear fit between model and data
     psphotSersicModelNorm (pcm, source);
+    if (!isfinite(PAR[PM_PAR_I0])) {
+        fprintf(stderr, "psphotSersicModelClassGuessPCM: psphotSerisicModelNorm set PM_PAR_I0 to NAN\n");
+        return false;
+    }
 
     if (TIMING) { t5 = psTimerMark ("SersicGuess"); }