diff --git a/web/app.js b/web/app.js
index 169af9ff1..6b8f41f1b 100644
--- a/web/app.js
+++ b/web/app.js
@@ -2155,27 +2155,23 @@ function webViewerResetPermissions() {
 }
 
 function webViewerPageRendered({ pageNumber, timestamp, error }) {
-  const pageIndex = pageNumber - 1;
-  const pageView = PDFViewerApplication.pdfViewer.getPageView(pageIndex);
-
   // If the page is still visible when it has finished rendering,
   // ensure that the page number input loading indicator is hidden.
   if (pageNumber === PDFViewerApplication.page) {
     PDFViewerApplication.toolbar.updateLoadingIndicatorState(false);
   }
 
-  // Prevent errors in the edge-case where the PDF document is removed *before*
-  // the 'pagerendered' event handler is invoked.
-  if (!pageView) {
-    return;
-  }
-
   // Use the rendered page to set the corresponding thumbnail image.
   if (PDFViewerApplication.pdfSidebar.isThumbnailViewVisible) {
-    const thumbnailView = PDFViewerApplication.pdfThumbnailViewer.getThumbnail(
-      pageIndex
+    const pageView = PDFViewerApplication.pdfViewer.getPageView(
+      /* index = */ pageNumber - 1
     );
-    thumbnailView.setImage(pageView);
+    const thumbnailView = PDFViewerApplication.pdfThumbnailViewer.getThumbnail(
+      /* index = */ pageNumber - 1
+    );
+    if (pageView && thumbnailView) {
+      thumbnailView.setImage(pageView);
+    }
   }
 
   if (error) {
@@ -2302,9 +2298,10 @@ function webViewerUpdateViewarea(evt) {
 
   // Show/hide the loading indicator in the page number input element.
   const currentPage = PDFViewerApplication.pdfViewer.getPageView(
-    PDFViewerApplication.page - 1
+    /* index = */ PDFViewerApplication.page - 1
   );
-  const loading = currentPage.renderingState !== RenderingStates.FINISHED;
+  const loading =
+    (currentPage && currentPage.renderingState) !== RenderingStates.FINISHED;
   PDFViewerApplication.toolbar.updateLoadingIndicatorState(loading);
 }
 
@@ -2549,14 +2546,12 @@ function webViewerRotationChanging(evt) {
   PDFViewerApplication.pdfViewer.currentPageNumber = evt.pageNumber;
 }
 
-function webViewerPageChanging(evt) {
-  const page = evt.pageNumber;
-
-  PDFViewerApplication.toolbar.setPageNumber(page, evt.pageLabel || null);
-  PDFViewerApplication.secondaryToolbar.setPageNumber(page);
+function webViewerPageChanging({ pageNumber, pageLabel }) {
+  PDFViewerApplication.toolbar.setPageNumber(pageNumber, pageLabel);
+  PDFViewerApplication.secondaryToolbar.setPageNumber(pageNumber);
 
   if (PDFViewerApplication.pdfSidebar.isThumbnailViewVisible) {
-    PDFViewerApplication.pdfThumbnailViewer.scrollThumbnailIntoView(page);
+    PDFViewerApplication.pdfThumbnailViewer.scrollThumbnailIntoView(pageNumber);
   }
 }