1 files changed, 1 insertions, 1 deletions
diff --git a/src/client/views/nodes/ComparisonBox.tsx b/src/client/views/nodes/ComparisonBox.tsx
index 72c7e4f45..15c33c8bf 100644
--- a/src/client/views/nodes/ComparisonBox.tsx
+++ b/src/client/views/nodes/ComparisonBox.tsx
@@ -89,7 +89,7 @@ export class ComparisonBox extends ViewBoxAnnotatableComponent<ViewBoxAnnotatabl
         };
         const displayDoc = (which: string) => {
             var whichDoc = Cast(this.dataDoc[which], Doc, null);
-            if (whichDoc.type === DocumentType.MARKER) whichDoc = Cast(whichDoc.annotationOn, Doc, null);
+            if (whichDoc?.type === DocumentType.MARKER) whichDoc = Cast(whichDoc.annotationOn, Doc, null);
             return whichDoc ? <>
                 <DocumentView {...OmitKeys(this.props, ["NativeWidth", "NativeHeight"]).omit}
                     isContentActive={returnFalse}