diff --git a/petab/v1/C.py b/petab/v1/C.py
index 2e3616ee..70ce22c3 100644
--- a/petab/v1/C.py
+++ b/petab/v1/C.py
@@ -2,8 +2,8 @@
 """
 This file contains constant definitions.
 """
-
 import math as _math
+import sys
 
 # MEASUREMENTS
 
@@ -363,3 +363,10 @@
 
 # separator for multiple parameter values (bounds, observableParameters, ...)
 PARAMETER_SEPARATOR = ";"
+
+
+__all__ = [
+    x
+    for x in dir(sys.modules[__name__])
+    if not x.startswith("_") and x not in {"sys", "math"}
+]
diff --git a/petab/v1/visualize/lint.py b/petab/v1/visualize/lint.py
index 0e973928..b5de74bc 100644
--- a/petab/v1/visualize/lint.py
+++ b/petab/v1/visualize/lint.py
@@ -1,4 +1,6 @@
 """Validation of PEtab visualization files"""
+from __future__ import annotations
+
 import logging
 
 import pandas as pd
@@ -8,6 +10,8 @@
 
 logger = logging.getLogger(__name__)
 
+__all__ = ["validate_visualization_df"]
+
 
 def validate_visualization_df(problem: Problem) -> bool:
     """Validate visualization table