diff --git a/datasalad/settings/env.py b/datasalad/settings/env.py
index 5df2347..6599568 100644
--- a/datasalad/settings/env.py
+++ b/datasalad/settings/env.py
@@ -44,7 +44,8 @@ def __init__(
         var_prefix: str | None = None,
     ):
         super().__init__()
-        self._var_prefix = var_prefix
+        self._var_prefix = var_prefix.upper() \
+            if os_name in ('os2', 'nt') else var_prefix
 
     def reinit(self):
         """Does nothing"""
@@ -56,6 +57,7 @@ def load(self) -> None:
         """
 
     def __getitem__(self, key: Hashable) -> Setting:
+        # TODO also support a mode where get_key_from_varname() is not implemented
         matching = {
             k: v
             for k, v in environ.items()