diff --git a/lib/RT/Test.pm b/lib/RT/Test.pm
index 003f3bc675d..cb6b597c3bd 100644
--- a/lib/RT/Test.pm
+++ b/lib/RT/Test.pm
@@ -1000,6 +1000,33 @@ sub load_or_create_custom_field {
     return $obj;
 }
 
+=head2 load_or_create_txn_custom_field
+
+=cut
+
+sub load_or_create_txn_custom_field {
+    my $self = shift;
+    my %args = ( Disabled => 0, @_ );
+    my $obj = RT::CustomField->new( RT->SystemUser );
+    if ( $args{'Name'} ) {
+        $obj->LoadByName(
+            Name       => $args{'Name'},
+            LookupType => RT::Transaction->CustomFieldLookupType,
+            ObjectId   => $args{'Queue'}->id,
+        );
+    } else {
+        die "Name is required";
+    }
+    unless ( $obj->id ) {
+        $args{'LookupType'} = 'RT::Queue-RT::Ticket-RT::Transaction';
+        my $queue = delete $args{'Queue'};
+        my ($val, $msg) = $obj->Create( %args );
+        $obj->AddToObject($queue);
+    }
+
+    return $obj;
+}
+
 sub last_ticket {
     my $self = shift;
     my $current = shift;
diff --git a/share/html/REST/1.0/Forms/ticket/comment b/share/html/REST/1.0/Forms/ticket/comment
index fb5c0d1deda..f95c82ac601 100644
--- a/share/html/REST/1.0/Forms/ticket/comment
+++ b/share/html/REST/1.0/Forms/ticket/comment
@@ -55,6 +55,8 @@ $id
 use MIME::Entity;
 use RT::Interface::REST;
 
+my $cf_spec = RT::Interface::REST->custom_field_spec(1);
+
 $RT::Logger->debug("Got ticket id=$id for comment");
 $RT::Logger->debug("Got args @{[keys(%changes)]}.");
 
@@ -78,7 +80,8 @@ unless ($action =~ /^(?:Comment|Correspond)$/) {
 }
 
 my $text = $changes{Text};
-my @atts = @{ vsplit($changes{Attachment}) };
+my @atts = @{ vsplit($changes{Attachment}) }
+    if defined $changes{Attachment};
 
 if (!$changes{Text} && @atts == 0) {
     $e = 1;
@@ -106,6 +109,20 @@ $ent->attach(
     }
 }
 
+{
+    my ($status, @msg) = $m->comp(
+        '/Elements/ValidateCustomFields',
+        CustomFields => $ticket->TransactionCustomFields,
+        Object => RT::Transaction->new( $session{'CurrentUser'} ),
+        ARGSRef => \%ARGS
+    );
+    unless ( $status ) {
+        $e = 1;
+        $c = "# " . join("\n# ", @msg);
+        goto OUTPUT;
+    }
+}
+
 unless ($ticket->CurrentUserHasRight('ModifyTicket') ||
         ($action eq "Comment" &&
          $ticket->CurrentUserHasRight("CommentOnTicket")) ||
@@ -117,18 +134,39 @@ unless ($ticket->CurrentUserHasRight('ModifyTicket') ||
     goto OUTPUT;
 }
 
-my $cc = join ", ", @{ vsplit($changes{Cc}) };
-my $bcc = join ", ", @{ vsplit($changes{Bcc}) };
-my ($n, $s) = $ticket->$action(MIMEObj => $ent,
-                               CcMessageTo => $cc,
-                               BccMessageTo => $bcc,
-                               TimeTaken => $changes{TimeWorked} || 0);
+my $cc = join ", ", @{ vsplit($changes{Cc} || '') };
+my $bcc = join ", ", @{ vsplit($changes{Bcc} || '') };
+my ($n, $s, $txn) = $ticket->$action(MIMEObj => $ent,
+                                     CcMessageTo => $cc,
+                                     BccMessageTo => $bcc,
+                                     TimeTaken => $changes{TimeWorked} || 0);
 $c = "# ".$s;
 if ($changes{Status}) {
    my  ($status_n, $status_s) = $ticket->SetStatus($changes{'Status'} );   
   $c .= "\n# ".$status_s;
 }
 
+my %v;
+foreach my $k (keys %changes) {
+    if ($k =~ /^$cf_spec/) {
+        my $key = $1 || $2;
+
+        my $cf = $txn->LoadCustomFieldByIdentifier($key);
+
+        if (not $cf->id) {
+            $c .= "\n# Invalid custom field name ($key)";
+            delete $changes{$k};
+            next;
+        }
+        if ($cf->SingleValue) {
+            $v{"CustomField-".$cf->Id()} = delete $changes{$k};
+        } else {
+            $v{"CustomField-".$cf->Id()} = vsplit(delete $changes{$k});
+        }
+    }
+}
+$txn->UpdateCustomFields(%v);
+
 OUTPUT:
 
 return [ $c, $o, $k, $e ];
diff --git a/share/html/REST/1.0/Forms/ticket/history b/share/html/REST/1.0/Forms/ticket/history
index cbb0ec38f24..67942bc1ce9 100644
--- a/share/html/REST/1.0/Forms/ticket/history
+++ b/share/html/REST/1.0/Forms/ticket/history
@@ -149,6 +149,37 @@ if ($tid) {
         push @data, [Attachments => $attachlist];
     }
 
+    # Display custom fields
+    my $CustomFields = $t->CustomFields;
+    while (my $cf = $CustomFields->Next()) {
+        next unless !%$fields
+                 || exists $fields->{"cf.{".lc($cf->Name)."}"}
+                 || exists $fields->{"cf-".lc $cf->Name};
+
+        my $vals = $t->CustomFieldValues($cf->Id());
+        my @out = ();
+        my $count = $vals->Count;
+        next unless $count;
+
+        if ( $count == 1) {
+            my $v = $vals->First;
+            push @out, $v->Content if $v;
+        }
+        else {
+            while (my $v = $vals->Next()) {
+                my $content = $v->Content;
+                if ( $v->Content =~ /,/ ) {
+                    $content =~ s/([\\'])/\\$1/g;
+                    push @out, q{'} . $content . q{'};
+                }
+                else {
+                    push @out, $content;
+                }
+            }
+        }
+        push @data, [ ('CF.{' . $cf->Name . '}') => join ',', @out ];
+    }
+
     my %k = map {@$_} @data;
     $o = [ map {$_->[0]} @data ];
     $k = \%k;
diff --git a/t/web/rest-txn-cf.t b/t/web/rest-txn-cf.t
new file mode 100644
index 00000000000..85ff4751a5b
--- /dev/null
+++ b/t/web/rest-txn-cf.t
@@ -0,0 +1,196 @@
+use strict;
+use warnings;
+use RT::Interface::REST;
+
+use RT::Test tests => 37;
+use Test::Warn;
+
+my ($baseurl, $m) = RT::Test->started_ok;
+
+my $queue = RT::Test->load_or_create_queue(Name => 'General');
+ok($queue->Id, "loaded the General queue");
+
+{
+    my $cf = RT::Test->load_or_create_txn_custom_field(
+        Name  => 'txn_cf',
+        Type  => 'FreeformSingle',
+        Queue => $queue,
+    );
+    ok($cf->Id, "created a CustomField: txn_cf");
+}
+{
+    my $cf = RT::Test->load_or_create_txn_custom_field(
+        Name  => 'txn_cf_multi',
+        Type  => 'FreeformMultiple',
+        Queue => $queue,
+    );
+    ok($cf->Id, "created a CustomField: txn_cf");
+}
+
+my $other_queue = RT::Test->load_or_create_queue(Name => 'Other Queue');
+ok($other_queue->Id, "loaded the Other Queue queue");
+
+{
+    my $cf = RT::Test->load_or_create_txn_custom_field(
+        Name  => 'txn_other_queue_cf',
+        Type  => 'FreeformSingle',
+        Queue => $other_queue,
+    );
+    ok($cf->Id, "created a CustomField");
+}
+
+$m->post("$baseurl/REST/1.0/ticket/new", [
+    user    => 'root',
+    pass    => 'password',
+    format  => 'l',
+]);
+
+my $text = $m->content;
+my @lines = $text =~ m{.*}g;
+shift @lines; # header
+
+ok($text =~ s/Subject:\s*$/Subject: REST interface/m, "successfully replaced subject");
+
+$m->post("$baseurl/REST/1.0/ticket/edit", [
+    user    => 'root',
+    pass    => 'password',
+
+    content => $text,
+], Content_Type => 'form-data');
+
+my ($id) = $m->content =~ /Ticket (\d+) created/;
+ok($id, "got ticket #$id");
+
+$text = join("\n", ( "Ticket: $id", "Action: correspond", "Content-Type: text/plain" ));
+$m->post(
+    "$baseurl/REST/1.0/ticket/$id/comment",
+    [
+        user => 'root',
+        pass => 'password',
+        content => "$text\nText: Test with no CF",
+    ],
+    Content_Type => 'form-data'
+);
+like($m->content, qr{Correspondence added}, "correspondance added - no CF");
+
+my $with_valid_cf = $text . "\nText: Test with valid CF\nCF.{txn_cf}: valid cf";
+
+$m->post(
+    "$baseurl/REST/1.0/ticket/$id/comment",
+    [
+        user => 'root',
+        pass => 'password',
+        content => $with_valid_cf,
+    ],
+    Content_Type => 'form-data'
+);
+like($m->content, qr{Correspondence added}, "correspondance added - valid CF");
+unlike($m->content, qr{Invalid custom field name}, "no invalid custom field - valid CF");
+
+my $ticket = RT::Ticket->new(RT->SystemUser);
+$ticket->Load($id);
+is($ticket->Id, $id, "loaded the REST-created ticket");
+is($ticket->Subject, "REST interface", "subject successfully set");
+
+my $txn = $ticket->Transactions->Last;
+my ($msg, @attachments) = @{$txn->Attachments->ItemsArrayRef};
+like($msg->Content, qr/Test with valid CF/, "Transaction contains expected content - valid CF");
+
+is($txn->FirstCustomFieldValue('txn_cf'), "valid cf", "CF successfully set - valid CF");
+
+$m->post(
+    "$baseurl/REST/1.0/ticket/$id/history",
+    [
+        user   => 'root',
+        pass   => 'password',
+        format => 'l',
+    ],
+    Content_Type => 'form-data'
+);
+
+like($m->content, qr/CF.\{txn_cf\}: valid cf/, "Ticket history contains expected content - valid CF");
+
+my $with_nonexistant_cf = $text . "\nText: Test with invalid CF\nCF.{other_cf}: invalid cf";
+
+$m->post(
+    "$baseurl/REST/1.0/ticket/$id/comment",
+    [
+        user => 'root',
+        pass => 'password',
+        content => $with_nonexistant_cf,
+    ],
+    Content_Type => 'form-data'
+);
+like($m->content, qr{Correspondence added}, "correspondance added - nonexistant CF");
+like($m->content, qr{Invalid custom field name}, "invalid custom field - nonexistant CF");
+
+$ticket->Load($id);
+is($ticket->Id, $id, "loaded the REST-created ticket");
+is($ticket->Subject, "REST interface", "subject successfully set");
+
+$txn = $ticket->Transactions->Last;
+($msg, @attachments) = @{$txn->Attachments->ItemsArrayRef};
+like($msg->Content, qr/Test with invalid CF/, "Transaction contains expected content - invalid CF");
+
+warning_like {$txn->FirstCustomFieldValue('other_cf')} qr"Couldn't load custom field by 'other_cf' identifier", "CF isn't set - invalid CF";
+
+my $with_other_queue_cf = $text . "\nText: Test with other queue CF\nCF.{txn_other_queue_cf}: invalid cf";
+
+$m->post(
+    "$baseurl/REST/1.0/ticket/$id/comment",
+    [
+        user => 'root',
+        pass => 'password',
+        content => $with_other_queue_cf,
+    ],
+    Content_Type => 'form-data'
+);
+like($m->content, qr{Correspondence added}, "correspondance added - other queue CF");
+like($m->content, qr{Invalid custom field name}, "invalid custom field - other queue CF");
+
+$ticket->Load($id);
+is($ticket->Id, $id, "loaded the REST-created ticket");
+is($ticket->Subject, "REST interface", "subject successfully set");
+
+$txn = $ticket->Transactions->Last;
+($msg, @attachments) = @{$txn->Attachments->ItemsArrayRef};
+like($msg->Content, qr/Test with other queue CF/, "Transaction contains expected content - other queue CF");
+
+warning_like {$txn->FirstCustomFieldValue('txn_other_queue_cf')} qr"Couldn't load custom field by 'txn_other_queue_cf' identifier", "CF isn't set - other queue CF";
+
+my $with_valid_cf_multi = $text . "\nText: Test with multi CF\nCF.{txn_cf_multi}: Value 1, Value 2";
+
+$m->post(
+    "$baseurl/REST/1.0/ticket/$id/comment",
+    [
+        user => 'root',
+        pass => 'password',
+        content => $with_valid_cf_multi,
+    ],
+    Content_Type => 'form-data'
+);
+like($m->content, qr{Correspondence added}, "correspondance added - valid CF multi");
+unlike($m->content, qr{Invalid custom field name}, "no invalid custom field - valid CF multi");
+
+$ticket = RT::Ticket->new(RT->SystemUser);
+$ticket->Load($id);
+is($ticket->Id, $id, "loaded the REST-created ticket - valid CF multi");
+is($ticket->Subject, "REST interface", "subject successfully set - valid CF multi");
+
+$txn = $ticket->Transactions->Last;
+($msg, @attachments) = @{$txn->Attachments->ItemsArrayRef};
+like($msg->Content, qr/Test with multi CF/, "Transaction contains expected content - valid CF multi");
+
+is($txn->FirstCustomFieldValue('txn_cf_multi'), "Value 1", "CF successfully set - valid CF multi");
+
+$m->post(
+    "$baseurl/REST/1.0/ticket/$id/history",
+    [
+        user   => 'root',
+        pass   => 'password',
+        format => 'l',
+    ],
+    Content_Type => 'form-data'
+);
+
+like($m->content, qr/CF.\{txn_cf_multi\}: Value 1,Value 2/, "Ticket history contains expected content - valid CF multi");