diff --git a/lib/src/models/documents/history.dart b/lib/src/models/documents/history.dart
index bdcd30d3..39173783 100644
--- a/lib/src/models/documents/history.dart
+++ b/lib/src/models/documents/history.dart
@@ -91,7 +91,7 @@ class History {
     }
     final delta = source.removeLast();
     // look for insert or delete
-    int len = 0;
+    var len = 0;
     final ops = delta.toList();
     for (var i = 0; i < ops.length; i++) {
       if ((ops[i].key == Operation.insertKey) ||