diff --git a/CHANGELOG.md b/CHANGELOG.md
index 278afc1823..591da356cf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fixed an exception in the authentication interceptor when the time zone of the browser is not available
+- Fixed the missing `userId` in the unique constraint of the `AccountBalance` database schema
 
 ## 3.86.0 - 2026-10-13
 
diff --git a/apps/api/src/app/account-balance/account-balance.service.ts b/apps/api/src/app/account-balance/account-balance.service.ts
index 56975cdf08..afa4386e01 100644
--- a/apps/api/src/app/account-balance/account-balance.service.ts
+++ b/apps/api/src/app/account-balance/account-balance.service.ts
@@ -68,9 +68,9 @@ export class AccountBalanceService {
         value: balance
       },
       where: {
-        userId,
-        accountId_date: {
+        accountId_userId_date: {
           accountId,
+          userId,
           date: resetHours(parseISO(date))
         }
       }
diff --git a/prisma/migrations/20261014000000_added_user_id_to_unique_constraint_of_account_balance/migration.sql b/prisma/migrations/20261014000000_added_user_id_to_unique_constraint_of_account_balance/migration.sql
new file mode 100644
index 0000000000..40c76e5816
--- /dev/null
+++ b/prisma/migrations/20261014000000_added_user_id_to_unique_constraint_of_account_balance/migration.sql
@@ -0,0 +1,5 @@
+-- DropIndex
+DROP INDEX "AccountBalance_accountId_date_key";
+
+-- CreateIndex
+CREATE UNIQUE INDEX "AccountBalance_accountId_userId_date_key" ON "AccountBalance"("accountId", "userId", "date");
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index e21fc10e8c..17a2d4e39d 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -65,7 +65,7 @@ model AccountBalance {
   userId    String
   value     Float
 
-  @@unique([accountId, date])
+  @@unique([accountId, userId, date])
   @@index([accountId])
   @@index([date])
 }