Index: generic/tclInt.h
==================================================================
--- generic/tclInt.h
+++ generic/tclInt.h
@@ -21,11 +21,11 @@
 
 /*
  * Some numerics configuration options.
  */
 
-#undef ACCEPT_NAN
+#define ACCEPT_NAN
 
 /*
  * In Tcl 8.7, stop supporting special hacks for legacy Itcl 3.
  * Itcl 4 doesn't need them. Itcl 3 can be updated to not need them
  * using the Tcl(Init|Reset)RewriteEnsemble() routines in all Tcl 8.6+