diff --git a/program/include/rcube_imap.inc b/program/include/rcube_imap.inc
index 50264acf0..9777d4c18 100644
--- a/program/include/rcube_imap.inc
+++ b/program/include/rcube_imap.inc
@@ -1478,10 +1478,10 @@ class rcube_imap
       $key,
       $index,
       $headers->uid,
-      substr((string)$this->decode_header($headers->subject, TRUE), 0, 128),
-      substr((string)$this->decode_header($headers->from, TRUE), 0, 128),
-      substr((string)$this->decode_header($headers->to, TRUE), 0, 128),
-      substr((string)$this->decode_header($headers->cc, TRUE), 0, 128),
+      (string)substr($this->decode_header($headers->subject, TRUE), 0, 128),
+      (string)substr($this->decode_header($headers->from, TRUE), 0, 128),
+      (string)substr($this->decode_header($headers->to, TRUE), 0, 128),
+      (string)substr($this->decode_header($headers->cc, TRUE), 0, 128),
       (int)$headers->size,
       serialize($headers));
     }