diff --git a/src-ui/src/app/components/document-detail/document-detail.component.ts b/src-ui/src/app/components/document-detail/document-detail.component.ts
index 2b839e969..75a64f548 100644
--- a/src-ui/src/app/components/document-detail/document-detail.component.ts
+++ b/src-ui/src/app/components/document-detail/document-detail.component.ts
@@ -49,7 +49,7 @@ export class DocumentDetailComponent implements OnInit {
   })
 
   previewCurrentPage: number = 1
-  previewNumPages: number
+  previewNumPages: number = 1
 
   constructor(
     private documentsService: DocumentService,