diff --git a/models/product.go b/models/product.go
index 5926fa6..78dff8e 100644
--- a/models/product.go
+++ b/models/product.go
@@ -21,11 +21,21 @@ type Productcount struct {
 	Outofstock int `json:"outofstock"`
 }
 
-// ProductCategoryUpdate is one row of a bulk re-filing: which product, and
-// which category it should sit in.
+// ProductCategoryUpdate is one row of a bulk re-filing: which product, which
+// category it sits in, and — the field that actually decides what a shopper
+// sees — which subcategory.
+//
+// Both are here because they do different jobs. GetProducts filters on
+// categoryid (the customer app asks for 2), while GetProductsBySubcategory
+// GROUPS on subcategoryid, so the aisle heading in the app comes from the
+// second and the first only decides whether the product is returned at all.
+// A caller re-filing products into aisles sends categoryid 2 unchanged and the
+// subcategory it worked out.
 type ProductCategoryUpdate struct {
 	Productid  int `json:"productid"`
 	Categoryid int `json:"categoryid"`
+	// Optional: 0 leaves whatever the product already has.
+	Subcategoryid int `json:"subcategoryid"`
 }
 
 type ProductCategory struct {
diff --git a/repositories/productRepository.go b/repositories/productRepository.go
index 9c51c18..2083b02 100644
--- a/repositories/productRepository.go
+++ b/repositories/productRepository.go
@@ -1429,7 +1429,7 @@ func (r *productRepository) RecategoriseProducts(tenantID int, updates []models.
 	}
 
 	placeholders := make([]string, 0, len(updates))
-	args := make([]any, 0, len(updates)*2)
+	args := make([]any, 0, len(updates)*3)
 	for _, u := range updates {
 		if u.Productid == 0 || u.Categoryid == 0 {
 			// categoryid 0 is the value the customer app rejects outright.
@@ -1437,18 +1437,27 @@ func (r *productRepository) RecategoriseProducts(tenantID int, updates []models.
 			// product from every shopper.
 			continue
 		}
-		placeholders = append(placeholders, "(?::bigint, ?::bigint)")
-		args = append(args, u.Productid, u.Categoryid)
+		placeholders = append(placeholders, "(?::bigint, ?::bigint, ?::bigint)")
+		args = append(args, u.Productid, u.Categoryid, u.Subcategoryid)
 	}
 	if len(placeholders) == 0 {
 		return 0, nil
 	}
 
+	// subcategoryid is written only when the caller sent one.
+	//
+	// It is the field the customer app groups by, so a 0 arriving from a caller
+	// that does not know about aisles would silently move a product back into
+	// the app's "Uncategorized" bucket. Zero therefore means "leave it alone",
+	// the same rule UpdateProductCategory already follows.
 	args = append(args, tenantID)
 	tx := r.db.Exec(`
 		UPDATE products p
-		SET categoryid = v.categoryid
-		FROM (VALUES `+strings.Join(placeholders, ",")+`) AS v(productid, categoryid)
+		SET categoryid = v.categoryid,
+		    subcategoryid = CASE WHEN v.subcategoryid > 0
+		                         THEN v.subcategoryid
+		                         ELSE p.subcategoryid END
+		FROM (VALUES `+strings.Join(placeholders, ",")+`) AS v(productid, categoryid, subcategoryid)
 		WHERE p.productid = v.productid
 		  AND p.tenantid = ?
 	`, args...)