diff --git a/src/vs/workbench/contrib/notebook/browser/diff/diffElementViewModel.ts b/src/vs/workbench/contrib/notebook/browser/diff/diffElementViewModel.ts
index 1e7d1fe38a7..793c7f89fa0 100644
--- a/src/vs/workbench/contrib/notebook/browser/diff/diffElementViewModel.ts
+++ b/src/vs/workbench/contrib/notebook/browser/diff/diffElementViewModel.ts
@@ -512,7 +512,9 @@ export class SideBySideDiffElementViewModel extends DiffElementCellViewModelBase
 				const modifiedMedataRaw = Object.assign({}, this.modified.metadata);
 				const originalCellMetadata = this.original.metadata;
 				for (const key of cellMetadataKeys) {
-					modifiedMedataRaw[key] = originalCellMetadata[key];
+					if (key in originalCellMetadata) {
+						modifiedMedataRaw[key] = originalCellMetadata[key];
+					}
 				}
 
 				this.modified.textModel.metadata = modifiedMedataRaw;