diff --git a/ext/js/templates/template-renderer.js b/ext/js/templates/template-renderer.js
index ae39e478..2db9e177 100644
--- a/ext/js/templates/template-renderer.js
+++ b/ext/js/templates/template-renderer.js
@@ -250,6 +250,7 @@ class TemplateRenderer {
 
         const tags = new Set();
         for (const tagSource of tagSources) {
+            if (!Array.isArray(tagSource)) { continue; }
             for (const tag of tagSource) {
                 tags.add(tag.name);
             }