proc ::tcl::clock::GetSystemTimeZone {} {
    variable TimeZoneBad

    if {[info exist ::env(TCL_TZ)]} {
	set timezone $::env(TCL_TZ)
    } elseif {[info exist ::env(TZ)]} {
	set timezone $::env(TZ)
    } elseif {![info exists timezone]} {
        # ask engine for the cached timezone:
        set timezone [configure -system-tz]
        if { $timezone ne "" } {
            return $timezone
        }
	if { $::tcl_platform(platform) eq {windows} } {
	    set timezone [GuessWindowsTimeZone]