diff --git a/crates/loro-core/src/dag/iter.rs b/crates/loro-core/src/dag/iter.rs
index c409244d..56a02113 100644
--- a/crates/loro-core/src/dag/iter.rs
+++ b/crates/loro-core/src/dag/iter.rs
@@ -245,7 +245,7 @@ impl<'a, T: DagNode + 'a, D: Dag<Node = T>> Iterator for DagCausalIter<'a, D> {
                         break;
                     }
                 }
-                (same_client, h.lamport)
+                (same_client, -(h.lamport as i32))
             });
             self.heap.pop().unwrap().id
         };