Index: trunk/psModules/src/objects/pmSourceFitModel.c
===================================================================
--- trunk/psModules/src/objects/pmSourceFitModel.c	(revision 32347)
+++ trunk/psModules/src/objects/pmSourceFitModel.c	(revision 34259)
@@ -182,4 +182,11 @@
         constraint->paramMask->data.PS_TYPE_VECTOR_MASK_DATA[PM_PAR_YPOS] = 1;
         constraint->paramMask->data.PS_TYPE_VECTOR_MASK_DATA[PM_PAR_SKY] = 1;
+        break;
+      case PM_SOURCE_FIT_TRAIL:
+        // special mode for pmModel_TRAIL: Io, Xo, Yo, Length, and Theta (not Io or Sigma)
+        nParams = params->n - 3;
+        psVectorInit (constraint->paramMask, 0);
+        constraint->paramMask->data.PS_TYPE_VECTOR_MASK_DATA[PM_PAR_SKY] = 1;
+        constraint->paramMask->data.PS_TYPE_VECTOR_MASK_DATA[PM_PAR_SIGMA] = 1;
         break;
       case PM_SOURCE_FIT_INDEX: