diff --git a/lib/gitlab/email/receiver.rb b/lib/gitlab/email/receiver.rb
index fa08b5c668f07fc0a1b9403c519bb5e01368dab9..b64db5d01ae43e44d1c899e4688855d324e8ac63 100644
--- a/lib/gitlab/email/receiver.rb
+++ b/lib/gitlab/email/receiver.rb
@@ -56,7 +56,9 @@ module Gitlab
       end
 
       def key_from_additional_headers(mail)
-        find_key_from_references(ensure_references_array(mail.references))
+        references = ensure_references_array(mail.references)
+
+        find_key_from_references(references)
       end
 
       def ensure_references_array(references)