diff --git a/application/Espo/Core/Mail/Importer/DefaultImporter.php b/application/Espo/Core/Mail/Importer/DefaultImporter.php
index 9bf198d21f..5491120c27 100644
--- a/application/Espo/Core/Mail/Importer/DefaultImporter.php
+++ b/application/Espo/Core/Mail/Importer/DefaultImporter.php
@@ -420,8 +420,8 @@ class DefaultImporter implements Importer
             $subject = '(No Subject)';
         }
 
-        if (strlen($subject) > self::SUBJECT_MAX_LENGTH) {
-            $subject = substr($subject, 0, self::SUBJECT_MAX_LENGTH);
+        if (mb_strlen($subject) > self::SUBJECT_MAX_LENGTH) {
+            $subject = mb_substr($subject, 0, self::SUBJECT_MAX_LENGTH);
         }
 
         return $subject;