diff --git a/reader/templates/reader/book_read/pdf_viewer.html b/reader/templates/reader/book_read/pdf_viewer.html
index 5fce1a9025a34c71afa8e9ad47f6e53ed9aabc4a..48425cabf40c7aadcf2243bdb67ceedbf689f5c9 100644
--- a/reader/templates/reader/book_read/pdf_viewer.html
+++ b/reader/templates/reader/book_read/pdf_viewer.html
@@ -651,9 +651,11 @@ See https://github.com/adobe-type-tools/cmap-resources
 
                 PDFViewerApplication.eventBus.on("pagechanging", (e) => {
                     console.log('pagechanging, from ' + e.previous + ' to ' + e.pageNumber);
-                    if (e.pageNumber === {{ pagenumber }}) {
-                        return;
-                    }
+                    {% if pagenumber %}
+                        if (e.pageNumber === {{ pagenumber }}) {
+                            return;
+                        }
+                    {% endif %}
                     $.ajax(
                         "{% url 'update_progress' book_id=book.id %}",
                         {