Index: generic/nsfError.c
===================================================================
diff -u -r2a16d792aa36cb6bfe4c212ae34aa43bb7c1013d -rc7b7511d348de756b5d3fff6b34795383cb0b458
--- generic/nsfError.c	(.../nsfError.c)	(revision 2a16d792aa36cb6bfe4c212ae34aa43bb7c1013d)
+++ generic/nsfError.c	(.../nsfError.c)	(revision c7b7511d348de756b5d3fff6b34795383cb0b458)
@@ -158,7 +158,7 @@
 
 #if defined(NDEBUG)
     if (unlikely(failure != 0)) {
-      fprintf(stderr, "writing string-formatting output to a dynamic Tcl string failed\n");
+      Tcl_Panic("writing string-formatting output to a dynamic Tcl string failed");
     }
 #endif
     assert(failure == 0);