diff --git a/mail/modules/MailUtils.jsm b/mail/modules/MailUtils.jsm
index b4a17ae1ce..2720be14b0 100644
--- a/mail/modules/MailUtils.jsm
+++ b/mail/modules/MailUtils.jsm
@@ -15,6 +15,9 @@ XPCOMUtils.defineLazyModuleGetters(lazy, {
   MailServices: "resource:///modules/MailServices.jsm",
   MimeParser: "resource:///modules/mimeParser.jsm",
   NetUtil: "resource://gre/modules/NetUtil.jsm",
+});
+
+ChromeUtils.defineESModuleGetters(lazy, {
   PluralForm: "resource:///modules/PluralForm.sys.mjs",
 });