diff --git a/CHANGES.md b/CHANGES.md
index ec8d6c95470..51bf82f3186 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,4 +1,5 @@
 # 6.5.12 2024-??-??
+  -2024-12-06 Fixed data evaluation in ICS calendar event.
  - 2024-11-28 Fixed Server Error, when Frontend::Template::GenerateBlockHooks###NAME has no valid data structure.
  - 2024-11-01 Fixed Bug - Translate the ticket state in PDF search result (AgentTicketSearch|CustomerTicketSearch). Thanks to @BuilderNSV for reporting the issue. [#615](https://github.com/znuny/Znuny/issues/615)
  - 2024-11-01 Sector Nord AG: Fixed uninitialized value in AdminSelectBox. Thanks to Sector Nord AG (@jsinagowitz). [PR#611](https://github.com/znuny/Znuny/pull/611)
diff --git a/Kernel/System/CalendarEvents/ICS.pm b/Kernel/System/CalendarEvents/ICS.pm
index 71d189b63b9..365ae9410df 100644
--- a/Kernel/System/CalendarEvents/ICS.pm
+++ b/Kernel/System/CalendarEvents/ICS.pm
@@ -284,10 +284,13 @@ sub _PrepareData {
 
                     my $Data = $Events{$EventID};
 
-                    my $DTStart      = $Data->{DTSTART};
-                    my $DTEnd        = $Data->{DTEND};
-                    my $DTStartLocal = $Data->{DTSTART}->{local_c};
-                    my $DTEndLocal   = $Data->{DTEND}->{local_c};
+                    my $DTStart = $Data->{DTSTART};
+                    my $DTEnd   = $Data->{DTEND};
+
+                    next EVENTID if ( ref $DTStart ne 'DateTime' ) || ( ref $DTEnd ne 'DateTime' );
+
+                    my $DTStartLocal = $DTStart->{local_c};
+                    my $DTEndLocal   = $DTEnd->{local_c};
 
                     my %Date = (
                         Start => {
@@ -374,10 +377,13 @@ sub _PrepareData {
                         }
                     }
 
-                    my $Organizer = $Data->{ORGANIZER}->{CN};
-                    if ($Organizer) {
+                    if (
+                        IsHashRefWithData( $Data->{ORGANIZER} )
+                        && IsStringWithData( $Data->{ORGANIZER}->{CN} )
+                        )
+                    {
                         my %Safety = $HTMLUtilsObject->Safety(
-                            String       => $Organizer,
+                            String       => $Data->{ORGANIZER}->{CN},
                             NoApplet     => 1,
                             NoObject     => 1,
                             NoEmbed      => 1,
@@ -420,13 +426,13 @@ sub _PrepareData {
                     }
 
                     for my $Property (qw(DESCRIPTION SUMMARY LOCATION)) {
-                        if ( $Data->{$Property} ) {
+                        if ( IsStringWithData( $Data->{$Property} ) ) {
                             $Data->{$Property} =~ s{\\n}{\n}g;
                             $Data->{$Property} =~ s{\\r}{\r}g;
                             $Data->{$Property} =~ s{&nbsp}{ }g;
                         }
                         my $PropertyString;
-                        if ( $Data->{$Property} ) {
+                        if ( IsStringWithData( $Data->{$Property} ) ) {
                             my %Safety = $HTMLUtilsObject->Safety(
                                 String       => $Data->{$Property},
                                 NoApplet     => 1,