diff --git a/mis_builder/__manifest__.py b/mis_builder/__manifest__.py
index 1ea8ca89f..987abd997 100644
--- a/mis_builder/__manifest__.py
+++ b/mis_builder/__manifest__.py
@@ -3,7 +3,7 @@
 
 {
     "name": "MIS Builder",
-    "version": "18.0.1.8.1",
+    "version": "18.0.1.8.2",
     "category": "Reporting",
     "summary": """
         Build 'Management Information System' Reports and Dashboards
diff --git a/mis_builder/migrations/18.0.1.8.2/post-migration.py b/mis_builder/migrations/18.0.1.8.2/post-migration.py
new file mode 100644
index 000000000..2e60a9bcb
--- /dev/null
+++ b/mis_builder/migrations/18.0.1.8.2/post-migration.py
@@ -0,0 +1,30 @@
+# Copyright 2026 Ledo Enterprises
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+import logging
+
+_logger = logging.getLogger(__name__)
+
+
+def migrate(cr, version):
+    """Recompute source_aml_model_id on mis.report.instance.period.
+
+    This stored computed field was introduced in 18.0 but existing periods
+    from earlier versions have NULL values, causing drilldown to fail with
+    'No view found for act_window action undefined'.
+    """
+    cr.execute(
+        """
+        UPDATE mis_report_instance_period p
+        SET source_aml_model_id = r.move_lines_source
+        FROM mis_report_instance i
+        JOIN mis_report r ON r.id = i.report_id
+        WHERE p.report_instance_id = i.id
+          AND p.source_aml_model_id IS NULL
+          AND r.move_lines_source IS NOT NULL
+        """
+    )
+    _logger.info(
+        "Recomputed source_aml_model_id on %d mis.report.instance.period records",
+        cr.rowcount,
+    )