diff --git a/src/tracksdata/graph/_rustworkx_graph.py b/src/tracksdata/graph/_rustworkx_graph.py
index ce009c3f..61adf1e6 100644
--- a/src/tracksdata/graph/_rustworkx_graph.py
+++ b/src/tracksdata/graph/_rustworkx_graph.py
@@ -1235,7 +1235,7 @@ def assign_tracklet_ids(
         else:
             if output_key not in self.node_attr_keys():
                 previous_id_df = None
-                self.add_node_attr_key(output_key, -1)
+                self.add_node_attr_key(output_key, pl.Int64, -1)
                 if tracklet_id_offset is None:
                     tracklet_id_offset = 1
             elif reset: