diff --git a/ext/fg/js/source.js b/ext/fg/js/source.js
index cbf0ce7d..bbf00e30 100644
--- a/ext/fg/js/source.js
+++ b/ext/fg/js/source.js
@@ -240,7 +240,7 @@ class TextSourceElement {
 
         let consumed = 0;
         let content = '';
-        for (let currentChar of this.content) {
+        for (let currentChar of this.content || '') {
             if (consumed >= length) {
                 break;
             } else if (!currentChar.match(IGNORE_TEXT_PATTERN)) {