diff --git a/fhem/lib/FHEM/Utility/CTZ.pm b/fhem/lib/FHEM/Utility/CTZ.pm
index 13854cb8d..7c87f864e 100644
--- a/fhem/lib/FHEM/Utility/CTZ.pm
+++ b/fhem/lib/FHEM/Utility/CTZ.pm
@@ -34,7 +34,7 @@ use strict;
 use warnings;
 use utf8;
 
-# use lib qw(/opt/fhem/FHEM  /opt/fhem/lib);                              # für Syntaxcheck mit: perl -c /opt/fhem/lib/FHEM/Utility/CTZ.pm
+ use lib qw(/opt/fhem/FHEM  /opt/fhem/lib);                              # für Syntaxcheck mit: perl -c /opt/fhem/lib/FHEM/Utility/CTZ.pm
 
 use GPUtils qw( GP_Import GP_Export );
 use DateTime;
@@ -89,7 +89,10 @@ sub convertTimeZone {
   my $writelog  = $paref->{writelog}  // 0;
   my $ms        = q{};
   
-  if ($dtstring =~ m/\.(\d+)/xs) {                       # datetime enthält Millisekunden                            
+  return "no valid timezone $tzcurrent" if(!checkValidName($tzcurrent));
+  return "no valid timezone $tzconv"    if(!checkValidName($tzconv)   );
+  
+  if ($dtstring =~ m/\.(\d+)/xs) {                                        # datetime enthält Millisekunden                            
       $ms = '.'.$1; 
   }
   
@@ -112,6 +115,14 @@ sub convertTimeZone {
 return ($err, $dtconv.$ms);
 }
 
+sub checkValidName {
+  my $tz = shift;
+  
+  my $valid = DateTime::TimeZone->is_valid_name($tz);
+          
+return $valid;
+}
+
 ###############################################################################
 # returns an array reference list of all possible time zone names
 ###############################################################################