diff --git a/.changeset/upset-mangos-stare.md b/.changeset/upset-mangos-stare.md
new file mode 100644
index 0000000000..495a82068b
--- /dev/null
+++ b/.changeset/upset-mangos-stare.md
@@ -0,0 +1,5 @@
+---
+"@medusajs/order": minor
+---
+
+fix(order): Add composite unique index on order_item version:item_id
diff --git a/packages/modules/order/src/migrations/.snapshot-medusa-order.json b/packages/modules/order/src/migrations/.snapshot-medusa-order.json
index c174cf53b5..6cf6e121e9 100644
--- a/packages/modules/order/src/migrations/.snapshot-medusa-order.json
+++ b/packages/modules/order/src/migrations/.snapshot-medusa-order.json
@@ -2005,6 +2005,15 @@
           "unique": false,
           "expression": "CREATE INDEX IF NOT EXISTS \"IDX_order_item_deleted_at\" ON \"order_item\" (\"deleted_at\") WHERE deleted_at IS NOT NULL"
         },
+        {
+          "keyName": "IDX_unique_order_item_version_item_id",
+          "columnNames": [],
+          "composite": false,
+          "constraint": false,
+          "primary": false,
+          "unique": false,
+          "expression": "CREATE UNIQUE INDEX IF NOT EXISTS \"IDX_unique_order_item_version_item_id\" ON \"order_item\" (\"version\", \"item_id\") WHERE deleted_at IS NULL"
+        },
         {
           "keyName": "order_item_pkey",
           "columnNames": [
diff --git a/packages/modules/order/src/migrations/Migration20251130184633.ts b/packages/modules/order/src/migrations/Migration20251130184633.ts
new file mode 100644
index 0000000000..a5cb4074a1
--- /dev/null
+++ b/packages/modules/order/src/migrations/Migration20251130184633.ts
@@ -0,0 +1,13 @@
+import { Migration } from '@mikro-orm/migrations';
+
+export class Migration20251130184633 extends Migration {
+
+  override async up(): Promise<void> {
+    this.addSql(`CREATE UNIQUE INDEX IF NOT EXISTS "IDX_unique_order_item_version_item_id" ON "order_item" ("version", "item_id") WHERE deleted_at IS NULL;`);
+  }
+
+  override async down(): Promise<void> {
+    this.addSql(`drop index if exists "IDX_unique_order_item_version_item_id";`);
+  }
+
+}
diff --git a/packages/modules/order/src/models/order-item.ts b/packages/modules/order/src/models/order-item.ts
index 753622204f..f16ff1bd2b 100644
--- a/packages/modules/order/src/models/order-item.ts
+++ b/packages/modules/order/src/models/order-item.ts
@@ -51,6 +51,12 @@ const _OrderItem = model
       unique: false,
       where: "deleted_at IS NOT NULL",
     },
+    {
+      name: "IDX_unique_order_item_version_item_id",
+      on: ["version", "item_id"],
+      unique: true,
+      where: "deleted_at IS NULL",
+    },
   ])
 
 export const OrderItem = _OrderItem