diff --git a/openupgrade_scripts/scripts/stock_account/19.0.1.1/post-migration.py b/openupgrade_scripts/scripts/stock_account/19.0.1.1/post-migration.py
index c90e05afd159..ad252f87384c 100644
--- a/openupgrade_scripts/scripts/stock_account/19.0.1.1/post-migration.py
+++ b/openupgrade_scripts/scripts/stock_account/19.0.1.1/post-migration.py
@@ -94,6 +94,122 @@ def stock_move_value(env):
     )
 
 
+def product_value_unit_cost(env):
+    """
+    Convert product.value#value from a total value to a unit cost where 19.0
+    expects one.
+
+    17.0 stock.valuation.layer#value held the *total* value of the layer, with
+    the per-unit price in the separate unit_cost column. 19.0
+    product.value#value is a unit cost for records not linked to a move: those
+    are what product.product#_get_last_product_value() reads to determine
+    standard_price. Records linked to a move keep total-value semantics and are
+    consumed by stock_move_value() above, so they are left alone -- which is
+    also why this has to run after it.
+
+    Without this, a move-less record keeps a total value where 19.0 reads a
+    unit cost, silently corrupting standard_price and every COGS entry derived
+    from it.
+
+    Two sources, in order of directness:
+
+    1. unit_cost, which pre-migration's rename_tables() leaves in place as an
+       orphan column. Exact wherever 17.0 populated it.
+    2. For manual revaluations 17.0 wrote unit_cost NULL and quantity 0, so the
+       unit cost is derived the same way 17.0 itself did in
+       product.product#_prepare_valuation_layer_field_values(): the running
+       sum(value) / sum(quantity) over the product's layers up to that point.
+       Evaluating it per record reproduces the historical cost at each record's
+       own date, which matters because _get_last_product_value() selects by
+       date.
+
+    Being an accumulation over the layers rather than a per-layer field, (2) is
+    cost-method independent and so covers fifo -- where a revaluation is spread
+    over the remaining_value of the layers still in stock and never lands in a
+    per-product unit cost -- as well as average.
+    """
+    # The accumulation in (2) sums the 17.0 total values, so snapshot them
+    # before (1) starts overwriting them with unit costs.
+    openupgrade.logged_query(
+        env.cr,
+        """
+        CREATE TEMPORARY TABLE openupgrade_17_layer_value AS
+        SELECT id, product_id, company_id, date, value, quantity
+          FROM product_value
+        """,
+    )
+    openupgrade.logged_query(
+        env.cr,
+        """
+        CREATE INDEX openupgrade_17_layer_value_idx
+            ON openupgrade_17_layer_value (product_id, company_id, date, id)
+        """,
+    )
+
+    openupgrade.logged_query(
+        env.cr,
+        """
+        UPDATE product_value
+           SET value = unit_cost
+         WHERE move_id IS NULL
+           AND quantity IS NOT NULL
+           AND unit_cost IS NOT NULL
+        """,
+    )
+    openupgrade.logged_query(
+        env.cr,
+        """
+        WITH computed AS (
+            SELECT target.id,
+                   sum(layer.value) / sum(layer.quantity) AS unit_cost
+              FROM product_value target
+              JOIN openupgrade_17_layer_value layer
+                ON layer.product_id = target.product_id
+               AND layer.company_id = target.company_id
+               AND (layer.date, layer.id) <= (target.date, target.id)
+             WHERE target.move_id IS NULL
+               AND target.quantity IS NOT NULL
+               AND target.unit_cost IS NULL
+             GROUP BY target.id
+            HAVING sum(layer.quantity) <> 0
+        )
+        UPDATE product_value
+           SET value = computed.unit_cost
+          FROM computed
+         WHERE product_value.id = computed.id
+        """,
+    )
+
+    # A product with no quantity on hand at that point has no meaningful unit
+    # cost to derive. Leave those alone and say so: a wrong standard_price is
+    # silent and ends up in the accounts, so guessing is worse than reporting.
+    env.cr.execute(
+        """
+        SELECT target.id, target.description
+          FROM product_value target
+          LEFT JOIN LATERAL (
+                SELECT sum(layer.quantity) AS quantity
+                  FROM openupgrade_17_layer_value layer
+                 WHERE layer.product_id = target.product_id
+                   AND layer.company_id = target.company_id
+                   AND (layer.date, layer.id) <= (target.date, target.id)
+               ) accumulated ON TRUE
+         WHERE target.move_id IS NULL
+           AND target.quantity IS NOT NULL
+           AND target.unit_cost IS NULL
+           AND coalesce(accumulated.quantity, 0) = 0
+        """
+    )
+    for value_id, description in env.cr.fetchall():
+        openupgrade.logger.warning(
+            "stock_account: product.value %s keeps its 17.0 total value because "
+            "the product had no quantity on hand to derive a unit cost from; "
+            "review it manually as it feeds standard_price. Description: %s",
+            value_id,
+            description,
+        )
+
+
 @openupgrade.migrate()
 def migrate(env, version):
     product_value_product_id(env)
@@ -101,3 +217,5 @@ def migrate(env, version):
     product_category_property_valuation(env)
     stock_location_valuation_account_id(env)
     stock_move_value(env)
+    # Must stay last: it rewrites the values stock_move_value() reads.
+    product_value_unit_cost(env)