diff --git a/app/javascript/src/javascripts/post_mode_menu.js b/app/javascript/src/javascripts/post_mode_menu.js
index 328a50043..0f29547ae 100644
--- a/app/javascript/src/javascripts/post_mode_menu.js
+++ b/app/javascript/src/javascripts/post_mode_menu.js
@@ -151,7 +151,7 @@ PostModeMenu.click = function(e) {
     Post.tag(post_id, "upvote:me");
   } else if (s === "tag-script") {
     var current_script_id = localStorage.getItem("current_tag_script_id");
-    var tag_script = localStorage.getItem("tag-script-" + current_script_id);
+    var tag_script = localStorage.getItem("tag-script-" + current_script_id) ?? "";
     Post.tag(post_id, tag_script);
   } else {
     return;
diff --git a/app/javascript/src/javascripts/posts.js.erb b/app/javascript/src/javascripts/posts.js.erb
index db4ac4be1..c1f5e4074 100644
--- a/app/javascript/src/javascripts/posts.js.erb
+++ b/app/javascript/src/javascripts/posts.js.erb
@@ -444,6 +444,7 @@ Post.show_pending_update_notice = function() {
 }
 
 Post.tag = function(post_id, tags) {
+  tags ??= "";
   const tag_string = (Array.isArray(tags) ? tags.join(" ") : String(tags));
   Post.update(post_id, "tag-script", { post: { old_tag_string: "", tag_string: tag_string }});
 }