diff --git a/src/DocumentIndex.js b/src/DocumentIndex.js
index 4f84cac..470acb5 100644
--- a/src/DocumentIndex.js
+++ b/src/DocumentIndex.js
@@ -13,9 +13,9 @@ class DocumentIndex {
 
   updateIndex (oplog, onProgressCallback) {
     const reducer = (handled, item, idx) => {
-      if (item.payload.op === 'PUTALL') {
+      if (item.payload.op === 'PUTALL' && item.payload.docs[Symbol.iterator]) {
         for (const doc of item.payload.docs) {
-          if (handled[doc.key] !== true) {
+          if (doc && handled[doc.key] !== true) {
             handled[doc.key] = true
             this._index[doc.key] = {
               op: item.payload.op,