Index: generic/nsf.c
===================================================================
diff -u -N -r9e6766c4da4c53a9c719d9a66286519e8984c053 -r1e69872805e0680718b270961aecc3d25b24612d
--- generic/nsf.c	(.../nsf.c)	(revision 9e6766c4da4c53a9c719d9a66286519e8984c053)
+++ generic/nsf.c	(.../nsf.c)	(revision 1e69872805e0680718b270961aecc3d25b24612d)
@@ -22976,6 +22976,8 @@
   NsfDStringVPrintf(&ds, fmt, ap);
   va_end(ap);
 
+  fprintf(stderr, "==== DEBUG AppVeyor: error msg<<%s>> (len %d)\n", ds.string, ds.length);
+
   if (tcd->onerror != NULL) {
     Tcl_Obj *script = Tcl_DuplicateObj(tcd->onerror);
     Tcl_Obj *cmd;