diff --git a/joint_buying_base/migrations/12.0.7.0.0/pre-migration.py b/joint_buying_base/migrations/12.0.7.0.0/pre-migration.py
new file mode 100644
index 00000000..b15e0a3a
--- /dev/null
+++ b/joint_buying_base/migrations/12.0.7.0.0/pre-migration.py
@@ -0,0 +1,37 @@
+# Copyright (C) 2024-Today: GRAP (http://www.grap.coop)
+# @author: Sylvain LE GAL (https://twitter.com/legalsylvain)
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+import logging
+
+from openupgradelib import openupgrade
+
+_logger = logging.getLogger(__name__)
+
+
+@openupgrade.migrate()
+def migrate(env, version):
+
+    _logger.info(
+        "Fix bad computation of joint_buying_transport_request.start_date field."
+    )
+    openupgrade.logged_query(
+        """
+    UPDATE joint_buying_transport_request tr_main
+    SET start_date = tmp.min_start_date
+    FROM (
+        SELECT tr.id as transport_request_id,
+        min(tl.start_date) as min_start_date
+        FROM joint_buying_transport_request tr
+        INNER JOIN joint_buying_transport_request_line trl
+            ON trl.request_id = tr.id
+        INNER JOIN joint_buying_tour_line tl
+            ON tl.id = trl.tour_line_id
+        WHERE tr.state = 'computed'
+        GROUP BY tr.id
+    ) as tmp
+    WHERE
+        tr_main.id = tmp.transport_request_id
+        AND tr_main.start_date != tmp.min_start_date;
+    """
+    )
diff --git a/joint_buying_base/models/joint_buying_transport_request.py b/joint_buying_base/models/joint_buying_transport_request.py
index 1d97956b..1b12df0d 100644
--- a/joint_buying_base/models/joint_buying_transport_request.py
+++ b/joint_buying_base/models/joint_buying_transport_request.py
@@ -291,7 +291,7 @@ def _set_tour_lines(self, tour_lines):
 
             self.write(
                 {
-                    "start_date": max(tour_lines.mapped("start_date")),
+                    "start_date": min(tour_lines.mapped("start_date")),
                     "arrival_date": max(tour_lines.mapped("arrival_date")),
                     "state": "computed",
                     "line_ids": [(5,)] + [(0, 0, x) for x in line_vals],