diff --git a/ehrapy/tools/_sa.py b/ehrapy/tools/_sa.py
index 684ea497..000d8fac 100644
--- a/ehrapy/tools/_sa.py
+++ b/ehrapy/tools/_sa.py
@@ -198,6 +198,7 @@ def kaplan_meier(
     adata: AnnData,
     duration_col: str,
     event_col: str | None = None,
+    *,
     timeline: list[float] | None = None,
     entry: str | None = None,
     label: str | None = None,
@@ -496,6 +497,7 @@ def nelson_aalen(
     adata: AnnData,
     duration_col: str,
     event_col: str | None = None,
+    *,
     timeline: list[float] | None = None,
     entry: str | None = None,
     label: str | None = None,
@@ -561,6 +563,7 @@ def weibull(
     adata: AnnData,
     duration_col: str,
     event_col: str,
+    *,
     timeline: list[float] | None = None,
     entry: str | None = None,
     label: str | None = None,