diff --git a/E01_StabRegister/E01_StabRegister_Source.py b/E01_StabRegister/E01_StabRegister_Source.py
index c8e5d9261..70bb98bb7 100644
--- a/E01_StabRegister/E01_StabRegister_Source.py
+++ b/E01_StabRegister/E01_StabRegister_Source.py
@@ -71,7 +71,7 @@ def db_snapshot(root: Path) -> dict[str, Any]:
 
 def _cross_rows(root: Path) -> list[dict[str, Any]]:
     rows = [row for row in db_snapshot(root)["cross_sections"] if row["chainage_m"] is not None]
-    return sorted(rows, key=lambda row: (float(row["chainage_m"]), row["sequence_num"] or 0))
+    return sorted(rows, key=lambda row: (float(row["chainage_m"]), row.get("sequence_num") or 0))
 
 
 def _row_data(row: dict[str, Any]) -> dict[str, Any]: