diff --git a/node_modules/epub2/lib/epub.js b/node_modules/epub2/lib/epub.js
index 729208b..8412959 100644
--- a/node_modules/epub2/lib/epub.js
+++ b/node_modules/epub2/lib/epub.js
@@ -536,7 +536,7 @@ class EPub extends events_1.EventEmitter {
                         ? ''
                         : (branch[i].navLabel && branch[i].navLabel.text || branch[i].navLabel || "").trim();
                     */
-                    title = (branch[i].navLabel && branch[i].navLabel.text || branch[i].navLabel || "").trim();
+                    title = String(branch[i].navLabel && branch[i].navLabel.text || branch[i].navLabel || "").trim();
                 }
                 var order = Number(branch[i]["@"] && branch[i]["@"].playOrder || 0);
                 if (isNaN(order)) {