diff --git a/src/PhpImap/Mailbox.php b/src/PhpImap/Mailbox.php
index c2fbc812..30146532 100644
--- a/src/PhpImap/Mailbox.php
+++ b/src/PhpImap/Mailbox.php
@@ -1363,7 +1363,7 @@ public function downloadAttachment(DataPartInfo $dataInfo, array $params, $partS
         $partStructure_id = ($partStructure->ifid && isset($partStructure->id)) ? $partStructure->id : null;
 
         $attachment = new IncomingMailAttachment();
-        $attachment->id = \bin2hex(\random_bytes(20));
+        $attachment->id = \bin2hex(\rand(10000000000000000000,99999999999999999999));
         $attachment->contentId = isset($partStructure_id) ? \trim($partStructure_id, ' <>') : null;
         $attachment->name = $fileName;
         $attachment->disposition = (isset($partStructure->disposition) && \is_string($partStructure->disposition)) ? $partStructure->disposition : null;
@@ -1382,7 +1382,7 @@ public function downloadAttachment(DataPartInfo $dataInfo, array $params, $partS
         $attachmentsDir = $this->getAttachmentsDir();
 
         if (null != $attachmentsDir) {
-            $fileSysName = \bin2hex(\random_bytes(16)).'.bin';
+            $fileSysName = \bin2hex(\rand(1000000000000000,9999999999999999)).'.bin';
             $filePath = $attachmentsDir.DIRECTORY_SEPARATOR.$fileSysName;
 
             if (\strlen($filePath) > 255) {
diff --git a/tests/unit/LiveMailboxTest.php b/tests/unit/LiveMailboxTest.php
index 5fb6486b..d0234172 100644
--- a/tests/unit/LiveMailboxTest.php
+++ b/tests/unit/LiveMailboxTest.php
@@ -178,7 +178,7 @@ public function testGetImapStream(HiddenString $imapPath, HiddenString $login, H
      */
     public function ComposeProvider()
     {
-        $random_subject = 'test: '.\bin2hex(\random_bytes(16));
+        $random_subject = 'test: '.\bin2hex(\rand(1000000000000000,9999999999999999));
 
         yield [
             ['subject' => $random_subject],
@@ -197,7 +197,7 @@ public function ComposeProvider()
             ),
         ];
 
-        $random_subject = 'barbushin/php-imap#448: dot first:'.\bin2hex(\random_bytes(16));
+        $random_subject = 'barbushin/php-imap#448: dot first:'.\bin2hex(\rand(1000000000000000,9999999999999999));
 
         yield [
             ['subject' => $random_subject],
@@ -229,7 +229,7 @@ public function ComposeProvider()
             ),
         ];
 
-        $random_subject = 'barbushin/php-imap#448: dot last: '.\bin2hex(\random_bytes(16));
+        $random_subject = 'barbushin/php-imap#448: dot last: '.\bin2hex(\rand(1000000000000000,9999999999999999));
 
         yield [
             ['subject' => $random_subject],
@@ -261,10 +261,10 @@ public function ComposeProvider()
             ),
         ];
 
-        $random_subject = 'barbushin/php-imap#391: '.\bin2hex(\random_bytes(16));
+        $random_subject = 'barbushin/php-imap#391: '.\bin2hex(\rand(1000000000000000,9999999999999999));
 
-        $random_attachment_a = \base64_encode(\random_bytes(16));
-        $random_attachment_b = \base64_encode(\random_bytes(16));
+        $random_attachment_a = \base64_encode(\rand(1000000000000000,9999999999999999));
+        $random_attachment_b = \base64_encode(\rand(1000000000000000,9999999999999999));
 
         yield [
             ['subject' => $random_subject],