diff --git a/CHANGELOG b/CHANGELOG
index 374d16bc9..012e94857 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -38,6 +38,7 @@ CHANGELOG Roundcube Webmail
 - Fix bug where Message-ID domain part was tied to username instead of current identity (#5385)
 - Fix bug where blocked.gif couldn't be attached to reply/forward with insecure content
 - Fix E_DEPRECATED warning when using Auth_SASL::factory() (#5401)
+- Fix bug where names of downloaded files could be mailformed when derived from the message subject (#5404)
 
 RELEASE 1.2.1
 -------------
diff --git a/plugins/zipdownload/zipdownload.php b/plugins/zipdownload/zipdownload.php
index 67c257988..8f7139db1 100644
--- a/plugins/zipdownload/zipdownload.php
+++ b/plugins/zipdownload/zipdownload.php
@@ -160,7 +160,8 @@ class zipdownload extends rcube_plugin
 
         $zip->close();
 
-        $filename = ($message->subject ?: 'roundcube') . '.zip';
+        $filename = ($this->_filename_from_subject($message->subject) ?: 'attachments') . '.zip';
+
         $this->_deliver_zipfile($tmpfname, $filename);
 
         // delete temporary files from disk
@@ -247,12 +248,11 @@ class zipdownload extends rcube_plugin
                     fwrite($tmpfp, "\r\n");
                 }
                 else { // maildir
-                    $subject = rcube_mime::decode_mime_string((string)$headers->subject);
+                    $subject = rcube_mime::decode_header($headers->subject, $headers->charset);
+                    $subject = $this->_filename_from_subject(mb_substr($subject, 0, 16));
                     $subject = $this->_convert_filename($subject);
-                    $subject = substr($subject, 0, 16);
 
-                    $disp_name = ($subject ?: 'message_rfc822') . ".eml";
-                    $disp_name = $path . $uid . "_" . $disp_name;
+                    $disp_name = $path . $uid . ($subject ? " $subject" : '') . '.eml';
 
                     $tmpfn = tempnam($temp_dir, 'zipmessage');
                     $tmpfp = fopen($tmpfn, 'w');
@@ -317,9 +317,19 @@ class zipdownload extends rcube_plugin
      */
     private function _convert_filename($str)
     {
-        $str = rcube_charset::convert($str, RCUBE_CHARSET, $this->charset);
+        $str = strtr($str, array(':' => '', '/' => '-'));
+
+        return rcube_charset::convert($str, RCUBE_CHARSET, $this->charset);
+    }
+
+    /**
+     * Helper function to convert message subject into filename
+     */
+    private function _filename_from_subject($str)
+    {
+        $str = preg_replace('/[\t\n\r\0\x0B]+\s*/', ' ', $str);
 
-        return strtr($str, array(':' => '', '/' => '-'));
+        return trim($str, " ./_");
     }
 }
 
diff --git a/program/steps/mail/viewsource.inc b/program/steps/mail/viewsource.inc
index 6dab45c6f..aa84bc2a0 100644
--- a/program/steps/mail/viewsource.inc
+++ b/program/steps/mail/viewsource.inc
@@ -41,14 +41,11 @@ if ($uid = rcube_utils::get_input_value('_uid', rcube_utils::INPUT_GET)) {
     header("Content-Type: text/plain; charset={$charset}");
 
     if (!empty($_GET['_save'])) {
-        $subject  = rcube_mime::decode_header($headers->subject, $headers->charset);
-        $filename = ($subject ?: $RCMAIL->config->get('product_name', 'email')) . '.eml';
         $browser  = $RCMAIL->output->browser;
-
-        if ($browser->ie)
-            $filename = rawurlencode($filename);
-        else
-            $filename = addcslashes($filename, '"');
+        $subject  = rcube_mime::decode_header($headers->subject, $headers->charset);
+        $filename = rcmail_filename_from_subject(mb_substr($subject, 0, 128));
+        $filename = ($filename ?: $uid)  . '.eml';
+        $filename = $browser->ie ? rawurlencode($filename) : addcslashes($filename, '"');
 
         header("Content-Length: {$headers->size}");
         header("Content-Disposition: attachment; filename=\"$filename\"");
@@ -73,3 +70,14 @@ else {
 }
 
 exit;
+
+
+/**
+ * Helper function to convert message subject into filename
+ */
+function rcmail_filename_from_subject($str)
+{
+    $str = preg_replace('/[:\t\n\r\0\x0B\/]+\s*/', ' ', $str);
+
+    return trim($str, " \t\n\r\0\x0B./_");
+}