diff --git a/docsource/modules180-190.rst b/docsource/modules180-190.rst
index a8d28c32350..18d8092c7b5 100644
--- a/docsource/modules180-190.rst
+++ b/docsource/modules180-190.rst
@@ -232,7 +232,7 @@ Module coverage 18.0 -> 19.0
 +---------------------------------------------------+----------------------+-------------------------------------------------+
 | http_routing                                      |Nothing to do         |                                                 |
 +---------------------------------------------------+----------------------+-------------------------------------------------+
-| iap                                               |Nothing to do         |No DB layout changes.                            |
+| iap                                               |Done                  |Backfill service_id from legacy service_name.    |
 +---------------------------------------------------+----------------------+-------------------------------------------------+
 | iap_crm                                           |                      |No DB layout changes.                            |
 +---------------------------------------------------+----------------------+-------------------------------------------------+
diff --git a/openupgrade_scripts/scripts/iap/19.0.1.1/post-migration.py b/openupgrade_scripts/scripts/iap/19.0.1.1/post-migration.py
new file mode 100644
index 00000000000..93a0efc839a
--- /dev/null
+++ b/openupgrade_scripts/scripts/iap/19.0.1.1/post-migration.py
@@ -0,0 +1,33 @@
+# Copyright 2026 Ledo
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+
+from openupgradelib import openupgrade
+
+
+@openupgrade.migrate()
+def migrate(env, version):
+    # the legacy prefix (openupgrade_legacy_<N>_0_*) depends on the DB's history
+    env.cr.execute(
+        """
+        SELECT column_name
+          FROM information_schema.columns
+         WHERE table_name = 'iap_account'
+           AND column_name LIKE 'openupgrade_legacy_%_service_name'
+         ORDER BY column_name
+         LIMIT 1
+        """
+    )
+    row = env.cr.fetchone()
+    if not row:
+        return
+    legacy_col = row[0]
+    openupgrade.logged_query(
+        env.cr,
+        f"""
+        UPDATE iap_account a
+        SET service_id = s.id
+        FROM iap_service s
+        WHERE a.service_id IS NULL
+          AND a.{legacy_col} = s.technical_name
+        """,
+    )
diff --git a/openupgrade_scripts/scripts/iap/tests/data_iap_migration.py b/openupgrade_scripts/scripts/iap/tests/data_iap_migration.py
new file mode 100644
index 00000000000..5f1d5453327
--- /dev/null
+++ b/openupgrade_scripts/scripts/iap/tests/data_iap_migration.py
@@ -0,0 +1,20 @@
+env = locals().get("env")
+
+# Recreate the upgrade-scarred shape (preserved legacy column + unlinked row)
+# so the post-migration backfill has rows to move on the fresh CI seed.
+env.cr.execute(
+    "ALTER TABLE iap_account "
+    "ADD COLUMN IF NOT EXISTS openupgrade_legacy_18_0_service_name varchar"
+)
+env.cr.execute("ALTER TABLE iap_account ALTER COLUMN service_id DROP NOT NULL")
+env.cr.execute(
+    """
+    INSERT INTO iap_account (openupgrade_legacy_18_0_service_name)
+    SELECT s.technical_name FROM iap_service s
+    WHERE NOT EXISTS (
+        SELECT 1 FROM iap_account
+        WHERE openupgrade_legacy_18_0_service_name IS NOT NULL)
+    LIMIT 1
+    """
+)
+env.cr.commit()