diff --git a/web/base_viewer.js b/web/base_viewer.js
index f73d876ba..0492241c3 100644
--- a/web/base_viewer.js
+++ b/web/base_viewer.js
@@ -1541,7 +1541,7 @@ class BaseViewer {
       if (!pageView.pdfPage) {
         pageView.setPdfPage(pdfPage);
       }
-      if (!this.linkService._cachedPageNumber(pdfPage.ref)) {
+      if (!this.linkService._cachedPageNumber?.(pdfPage.ref)) {
         this.linkService.cachePageRef(pageView.id, pdfPage.ref);
       }
       return pdfPage;