diff --git a/CHANGELOG b/CHANGELOG
index 3e319595a..6d7a6a513 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -40,6 +40,7 @@ CHANGELOG Roundcube Webmail
 - Elastic: Fix unwanted thread expanding when selecting a collapsed thread in non-mobile mode (#6445)
 - Elastic: Add "status bar" for mobile in mail composer
 - Log errors caused by low pcre.backtrack_limit when sending a mail message (#6433)
+- Fix so max_message_size limit is checked also when forwarding messages as attachments (#6580)
 - Fix so performance stats are logged to the main console log also when per_user_logging=true
 - Fix malformed message saved into Sent folder when using big attachments and low memory limit (#6498)
 - Fix incorrect IMAP SASL GSSAPI negotiation (#6308)
diff --git a/program/include/rcmail_output_html.php b/program/include/rcmail_output_html.php
index 761d2755e..c35ff54ae 100644
--- a/program/include/rcmail_output_html.php
+++ b/program/include/rcmail_output_html.php
@@ -1706,7 +1706,7 @@ EOF;
      * Add inline javascript code
      *
      * @param string $script   JS code snippet
-     * @param string $position Target position [head|head_top|foot]
+     * @param string $position Target position [head|head_top|foot|docready]
      */
     public function add_script($script, $position = 'head')
     {
diff --git a/program/localization/en_US/messages.inc b/program/localization/en_US/messages.inc
index 441bfa137..7b3356354 100644
--- a/program/localization/en_US/messages.inc
+++ b/program/localization/en_US/messages.inc
@@ -129,6 +129,7 @@ $messages['fileuploaderror'] = 'File upload failed.';
 $messages['filesizeerror'] = 'The uploaded file exceeds the maximum size of $size.';
 $messages['filecounterror'] = 'You can upload maximum $count files at once.';
 $messages['msgsizeerror'] = 'Failed to attach a file. Maximum size of a message ($size) exceeded.';
+$messages['msgsizeerrorfwd'] = 'Maximum size of a message ($size) exceeded. $num message(s) have not been attached.';
 $messages['copysuccess'] = 'Successfully copied $nr contacts.';
 $messages['movesuccess'] = 'Successfully moved $nr contacts.';
 $messages['copyerror'] = 'Could not copy any contacts.';
diff --git a/program/steps/mail/compose.inc b/program/steps/mail/compose.inc
index b00936d6e..6ae288aa7 100644
--- a/program/steps/mail/compose.inc
+++ b/program/steps/mail/compose.inc
@@ -1033,17 +1033,21 @@ function rcmail_write_forward_attachments()
 {
     global $RCMAIL, $COMPOSE, $MESSAGE;
 
-    $storage = $RCMAIL->get_storage();
-    $names   = array();
-    $refs    = array();
-
     if ($MESSAGE->pgp_mime) {
         return;
     }
 
+    $storage     = $RCMAIL->get_storage();
+    $names       = array();
+    $refs        = array();
+    $size_errors = 0;
+    $size_limit  = parse_bytes($RCMAIL->config->get('max_message_size'));
+    $total_size  = 10 * 1024; // size of message body, to start with
+
     $loaded_attachments = array();
     foreach ((array)$COMPOSE['attachments'] as $attachment) {
         $loaded_attachments[$attachment['name'] . $attachment['mimetype']] = $attachment;
+        $total_size += $attachment['size'];
     }
 
     if ($COMPOSE['forward_uid'] == '*') {
@@ -1085,6 +1089,13 @@ function rcmail_write_forward_attachments()
             continue;
         }
 
+        if ($size_limit && $size_limit < $total_size + $message->headers->size) {
+            $size_errors++;
+            continue;
+        }
+
+        $total_size += $message->headers->size;
+
         rcmail_save_attachment($message, null, $COMPOSE['id'], array('filename' => $name));
 
         if ($message->headers->messageID) {
@@ -1096,9 +1107,16 @@ function rcmail_write_forward_attachments()
     if (count($refs) == 1) {
         $COMPOSE['reply_msgid'] = $refs[0];
     }
+
     if (!empty($refs)) {
         $COMPOSE['references'] = implode(' ', $refs);
     }
+
+    if ($size_errors) {
+        $limit = $RCMAIL->show_bytes($size_limit);
+        $error = $RCMAIL->gettext(array('name' => 'msgsizeerrorfwd', 'vars' => array('num' => $size_errors, 'size' => $limit)));
+        $RCMAIL->output->add_script(sprintf("%s.display_message('%s', 'error');", rcmail_output::JS_OBJECT_NAME, rcube::JQ($error)), 'docready');
+    }
 }
 
 // Saves an image as attachment