diff --git a/src/ytype.js b/src/ytype.js
index 52485272..720bf3d9 100644
--- a/src/ytype.js
+++ b/src/ytype.js
@@ -1047,7 +1047,7 @@ export class YType {
             deleteText(transaction, currPos, op.delete)
           } else if (delta.$modifyOp.check(op)) {
             let item = currPos.right
-            while (item?.deleted && !item.countable) { item = item.next }
+            while (item != null && (item.deleted || !item.countable)) { item = item.next }
             if (item == null || item.content.constructor !== ContentType) { error.unexpectedCase() }
             /** @type {ContentType} */ (item.content).type.applyDelta(op.value)
             currPos.formatText(transaction, /** @type {any} */ (this), 1, op.format || {})