diff --git a/src/agora/utils/merge.py b/src/agora/utils/merge.py
index 8db36bb35dfeab9feb1db1c3d2d85153285d99b7..183acbdeeb0b525141659ffa4ce6d0ecd46cac1e 100644
--- a/src/agora/utils/merge.py
+++ b/src/agora/utils/merge.py
@@ -96,6 +96,8 @@ def merge_lineage(
             replacement_dict[tuple(index)]
             for index in flat_lineage[valid_lineages]
         ]
+    else:
+        new_merges = merges
     # reverse flattening
     new_lineage = flat_lineage.reshape(-1, 2, 2)
     # remove any duplicates