Index: generic/tclClock.c
==================================================================
--- generic/tclClock.c
+++ generic/tclClock.c
@@ -237,11 +237,11 @@
 
     data->lastBase.timezoneObj = NULL;
 
     memset(&data->lastTZOffsCache, 0, sizeof(data->lastTZOffsCache));
 
-    data->defFlags = 0;
+    data->defFlags = CLF_VALIDATE;
 
     /*
      * Install the commands.
      */