Index: /trunk/psphot/src/psphotFitSourcesLinear.c
===================================================================
--- /trunk/psphot/src/psphotFitSourcesLinear.c	(revision 37554)
+++ /trunk/psphot/src/psphotFitSourcesLinear.c	(revision 37555)
@@ -263,4 +263,10 @@
 	    }
 	}
+        if (modelSum == 0 ||  maskedSum == 0) {
+            // no pixels at all drop the modelPSF (probably only an issue for external sources
+            // which are created from a fake peak (full force))
+            psFree(source->modelPSF);
+            continue;
+        }
 	if (modelSum < 0.5) continue; // skip sources with no model constraint (somewhat arbitrary limit)
 	if (modelSum < 0.8) {