diff --git a/src/earthkit/data/sources/mars.py b/src/earthkit/data/sources/mars.py
index 22369415..89868bd3 100644
--- a/src/earthkit/data/sources/mars.py
+++ b/src/earthkit/data/sources/mars.py
@@ -52,7 +52,6 @@ def execute(self, request, target, log=None):
 
             subprocess.run(
                 [self.command(), filename],
-                env=dict(os.environ, MARS_AUTO_SPLIT_BY_DATES="1"),
                 check=True,
                 **log,
             )