diff --git a/wagtail_modeltranslation/static/wagtail_modeltranslation/js/wagtail_translated_slugs.js b/wagtail_modeltranslation/static/wagtail_modeltranslation/js/wagtail_translated_slugs.js
index ea14a69..5b60bd1 100644
--- a/wagtail_modeltranslation/static/wagtail_modeltranslation/js/wagtail_translated_slugs.js
+++ b/wagtail_modeltranslation/static/wagtail_modeltranslation/js/wagtail_translated_slugs.js
@@ -4,6 +4,7 @@ $(document).ready(function () {
         var slugFollowsTitle = false;
 
         $.each(langs, function (idx, lang_code) {
+            lang_code = lang_code.replace("-", "_");
             $('#id_title_' + lang_code).on('focus', function () {
                 /* slug should only follow the title field if its value matched the title's value at the time of focus */
                 var currentSlug = $('#id_slug_' + lang_code).val();
@@ -19,4 +20,4 @@ $(document).ready(function () {
             });
         });
     }
-});
\ No newline at end of file
+});