diff --git a/go.mod b/go.mod
index 57507d0fe..b7dc25055 100644
--- a/go.mod
+++ b/go.mod
@@ -86,7 +86,7 @@ require (
 	github.com/buger/jsonparser v1.1.1 // indirect
 	github.com/cenkalti/backoff/v4 v4.3.0 // indirect
 	github.com/containerd/continuity v0.4.3 // indirect
-	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
+	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc
 	github.com/dlclark/regexp2 v1.11.4 // indirect
 	github.com/dnwe/otelsarama v0.0.0-20240308230250-9388d9d40bc0 // indirect
 	github.com/docker/cli v27.3.1+incompatible // indirect
diff --git a/internal/controller/ledger/store_generated_test.go b/internal/controller/ledger/store_generated_test.go
index 1618ae7c3..59479b0da 100644
--- a/internal/controller/ledger/store_generated_test.go
+++ b/internal/controller/ledger/store_generated_test.go
@@ -364,7 +364,7 @@ func (mr *MockStoreMockRecorder) GetVolumesWithBalances(ctx, q any) *gomock.Call
 // IsUpToDate mocks base method.
 func (m *MockStore) IsUpToDate(ctx context.Context) (bool, error) {
 	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "IsUpToDate", ctx)
+	ret := m.ctrl.Call(m, "HasMinimalVersion", ctx)
 	ret0, _ := ret[0].(bool)
 	ret1, _ := ret[1].(error)
 	return ret0, ret1
@@ -373,7 +373,7 @@ func (m *MockStore) IsUpToDate(ctx context.Context) (bool, error) {
 // IsUpToDate indicates an expected call of IsUpToDate.
 func (mr *MockStoreMockRecorder) IsUpToDate(ctx any) *gomock.Call {
 	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "IsUpToDate", reflect.TypeOf((*MockStore)(nil).IsUpToDate), ctx)
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "HasMinimalVersion", reflect.TypeOf((*MockStore)(nil).IsUpToDate), ctx)
 }
 
 // ListAccounts mocks base method.
diff --git a/internal/storage/bucket/bucket.go b/internal/storage/bucket/bucket.go
index ef1347243..8db0c7dda 100644
--- a/internal/storage/bucket/bucket.go
+++ b/internal/storage/bucket/bucket.go
@@ -24,7 +24,7 @@ func (b *Bucket) Migrate(ctx context.Context, tracer trace.Tracer) error {
 	return migrate(ctx, tracer, b.db, b.name)
 }
 
-func (b *Bucket) IsUpToDate(ctx context.Context) (bool, error) {
+func (b *Bucket) HasMinimalVersion(ctx context.Context) (bool, error) {
 	migrator := GetMigrator(b.db, b.name)
 	lastVersion, err := migrator.GetLastVersion(ctx)
 	if err != nil {
diff --git a/internal/storage/bucket/migrations/11-make-stateless/up.sql b/internal/storage/bucket/migrations/11-make-stateless/up.sql
index 9b92f4282..b8d2c9666 100644
--- a/internal/storage/bucket/migrations/11-make-stateless/up.sql
+++ b/internal/storage/bucket/migrations/11-make-stateless/up.sql
@@ -513,3 +513,35 @@ $do$
 		end loop;
 	END
 $do$;
+
+-- following index will enforce uniqueness of transaction reference until the appropriate index is full built (see next migration)
+create or replace function enforce_reference_uniqueness() returns trigger
+	security definer
+	language plpgsql
+as
+$$
+begin
+	-- Temporary magic number
+	-- The migration 13 will remove the trigger
+	perform pg_advisory_xact_lock(9999999);
+
+	if exists(
+		select 1
+		from transactions
+		where reference = new.reference
+			and ledger = new.ledger
+			and id != new.id
+	) then
+		raise exception 'duplicate reference';
+	end if;
+
+	return new;
+end
+$$ set search_path from current;
+
+create constraint trigger enforce_reference_uniqueness
+after insert on transactions
+deferrable initially deferred
+for each row
+when ( new.reference is not null )
+execute procedure enforce_reference_uniqueness();
\ No newline at end of file
diff --git a/internal/storage/bucket/migrations/13-create-ledger-indexes/up.sql b/internal/storage/bucket/migrations/13-create-ledger-indexes/up.sql
index 1efb24192..5fa90936e 100644
--- a/internal/storage/bucket/migrations/13-create-ledger-indexes/up.sql
+++ b/internal/storage/bucket/migrations/13-create-ledger-indexes/up.sql
@@ -1,5 +1,8 @@
 set search_path = '{{.Schema}}';
 
+drop trigger enforce_reference_uniqueness on transactions;
+drop function enforce_reference_uniqueness();
+
 drop index transactions_reference;
 alter index transactions_reference2 rename to transactions_reference;
 
diff --git a/internal/storage/driver/driver.go b/internal/storage/driver/driver.go
index 7dd772242..a260fdfdf 100644
--- a/internal/storage/driver/driver.go
+++ b/internal/storage/driver/driver.go
@@ -216,6 +216,10 @@ func (d *Driver) UpgradeAllBuckets(ctx context.Context) error {
 	return nil
 }
 
+func (d *Driver) GetDB() *bun.DB {
+	return d.db
+}
+
 func New(db *bun.DB, opts ...Option) *Driver {
 	ret := &Driver{
 		db: db,
diff --git a/internal/storage/ledger/legacy/adapters.go b/internal/storage/ledger/legacy/adapters.go
index 3d94a53f9..4fa415d2d 100644
--- a/internal/storage/ledger/legacy/adapters.go
+++ b/internal/storage/ledger/legacy/adapters.go
@@ -116,7 +116,7 @@ func (d *DefaultStoreAdapter) GetVolumesWithBalances(ctx context.Context, q ledg
 }
 
 func (d *DefaultStoreAdapter) IsUpToDate(ctx context.Context) (bool, error) {
-	return d.newStore.IsUpToDate(ctx)
+	return d.newStore.HasMinimalVersion(ctx)
 }
 
 func (d *DefaultStoreAdapter) GetMigrationsInfo(ctx context.Context) ([]migrations.Info, error) {
diff --git a/internal/storage/ledger/main_test.go b/internal/storage/ledger/main_test.go
index 7670169d9..21b923a44 100644
--- a/internal/storage/ledger/main_test.go
+++ b/internal/storage/ledger/main_test.go
@@ -8,16 +8,13 @@ import (
 	. "github.com/formancehq/go-libs/v2/testing/utils"
 	"github.com/formancehq/ledger/internal/storage/driver"
 	ledgerstore "github.com/formancehq/ledger/internal/storage/ledger"
-	"go.opentelemetry.io/otel/trace/noop"
 	"math/big"
 	"os"
-	"sync/atomic"
 	"testing"
 
 	"github.com/formancehq/go-libs/v2/bun/bundebug"
 	"github.com/formancehq/go-libs/v2/testing/docker"
 	ledger "github.com/formancehq/ledger/internal"
-	"github.com/formancehq/ledger/internal/storage/bucket"
 	"github.com/google/go-cmp/cmp"
 
 	"github.com/uptrace/bun/dialect/pgdialect"
@@ -33,7 +30,6 @@ import (
 var (
 	srv         = NewDeferred[*pgtesting.PostgresServer]()
 	bunDB       = NewDeferred[*bun.DB]()
-	ledgerCount = atomic.Int64{}
 )
 
 func TestMain(m *testing.M) {
@@ -68,10 +64,9 @@ type T interface {
 	Cleanup(func())
 }
 
-func newLedgerStore(t T) *ledgerstore.Store {
+func newDriver(t T) *driver.Driver {
 	t.Helper()
 
-	ledgerName := uuid.NewString()[:8]
 	ctx := logging.TestingContext()
 
 	Wait(srv, bunDB)
@@ -88,15 +83,23 @@ func newLedgerStore(t T) *ledgerstore.Store {
 
 	require.NoError(t, driver.Migrate(ctx, db))
 
+	return driver.New(bunDB.GetValue())
+}
+
+func newLedgerStore(t T) *ledgerstore.Store {
+	t.Helper()
+
+	driver := newDriver(t)
+	ledgerName := uuid.NewString()[:8]
+	ctx := logging.TestingContext()
+
 	l := ledger.MustNewWithDefault(ledgerName)
 	l.Bucket = ledgerName
-	l.ID = int(ledgerCount.Add(1))
 
-	b := bucket.New(bunDB.GetValue(), ledgerName)
-	require.NoError(t, b.Migrate(ctx, noop.Tracer{}))
-	require.NoError(t, b.AddLedger(ctx, l, bunDB.GetValue()))
+	store, err := driver.CreateLedger(ctx, &l)
+	require.NoError(t, err)
 
-	return ledgerstore.New(bunDB.GetValue(), b, l)
+	return store
 }
 
 func bigIntComparer(v1 *big.Int, v2 *big.Int) bool {
diff --git a/internal/storage/ledger/store.go b/internal/storage/ledger/store.go
index d7611c114..26d2f6e05 100644
--- a/internal/storage/ledger/store.go
+++ b/internal/storage/ledger/store.go
@@ -186,8 +186,8 @@ func New(db bun.IDB, bucket *bucket.Bucket, ledger ledger.Ledger, opts ...Option
 	return ret
 }
 
-func (s *Store) IsUpToDate(ctx context.Context) (bool, error) {
-	return s.bucket.IsUpToDate(ctx)
+func (s *Store) HasMinimalVersion(ctx context.Context) (bool, error) {
+	return s.bucket.HasMinimalVersion(ctx)
 }
 
 func (s *Store) GetMigrationsInfo(ctx context.Context) ([]migrations.Info, error) {
diff --git a/internal/storage/ledger/transactions.go b/internal/storage/ledger/transactions.go
index 801b1ef18..40c93c5fb 100644
--- a/internal/storage/ledger/transactions.go
+++ b/internal/storage/ledger/transactions.go
@@ -240,6 +240,25 @@ func (s *Store) selectTransactions(date *time.Time, expandVolumes, expandEffecti
 }
 
 func (s *Store) CommitTransaction(ctx context.Context, tx *ledger.Transaction) error {
+
+	// todo(next-minor): remove that on ledger 2.3 when the corresponding index will be completely built (see migration 12)
+	//if tx.Reference != "" {
+	//	// Magic number, as long as no other process try to take the same exact lock for another reason, it will be ok.
+	//	// This code will be removed in the next minor by the way.
+	//	_, err := s.db.ExecContext(ctx, `select pg_advisory_xact_lock(99999999999)`)
+	//	if err != nil {
+	//		return err
+	//	}
+	//
+	//	exists, err := s.db.NewSelect().
+	//		ModelTableExpr(s.GetPrefixedRelationName("transactions")).
+	//		Where("reference = ?", tx.Reference).
+	//		Exists(ctx)
+	//	if exists {
+	//		return ledgercontroller.NewErrTransactionReferenceConflict(tx.Reference)
+	//	}
+	//}
+
 	postCommitVolumes, err := s.UpdateVolumes(ctx, tx.VolumeUpdates()...)
 	if err != nil {
 		return fmt.Errorf("failed to update balances: %w", err)
@@ -400,6 +419,11 @@ func (s *Store) InsertTransaction(ctx context.Context, tx *ledger.Transaction) e
 					if err.(postgres.ErrConstraintsFailed).GetConstraint() == "transactions_reference" {
 						return nil, ledgercontroller.NewErrTransactionReferenceConflict(tx.Reference)
 					}
+				case errors.Is(err, postgres.ErrRaisedException{}):
+					// todo(next-minor): remove this test
+					if err.(postgres.ErrRaisedException).GetMessage() == "duplicate reference" {
+						return nil, ledgercontroller.NewErrTransactionReferenceConflict(tx.Reference)
+					}
 				default:
 					return nil, err
 				}
diff --git a/internal/storage/ledger/transactions_test.go b/internal/storage/ledger/transactions_test.go
index 129debaf0..5978f51a0 100644
--- a/internal/storage/ledger/transactions_test.go
+++ b/internal/storage/ledger/transactions_test.go
@@ -7,6 +7,9 @@ import (
 	"database/sql"
 	"fmt"
 	"github.com/alitto/pond"
+	"github.com/formancehq/ledger/internal/storage/bucket"
+	ledgerstore "github.com/formancehq/ledger/internal/storage/ledger"
+	"github.com/google/uuid"
 	"math/big"
 	"slices"
 	"testing"
@@ -603,6 +606,84 @@ func TestTransactionsInsert(t *testing.T) {
 		require.Error(t, err)
 		require.True(t, errors.Is(err, ledgercontroller.ErrTransactionReferenceConflict{}))
 	})
+	// todo(next-minor): remove this test
+	t.Run("check reference conflict with minimal store version", func(t *testing.T) {
+		t.Parallel()
+
+		driver := newDriver(t)
+		ledgerName := uuid.NewString()[:8]
+
+		l := ledger.MustNewWithDefault(ledgerName)
+		l.Bucket = ledgerName
+
+		migrator := bucket.GetMigrator(driver.GetDB(), ledgerName)
+		for i := 0; i < bucket.MinimalSchemaVersion; i++ {
+			require.NoError(t, migrator.UpByOne(ctx))
+		}
+
+		b := bucket.New(driver.GetDB(), ledgerName)
+		err := b.AddLedger(ctx, l, driver.GetDB())
+		require.NoError(t, err)
+
+		store := ledgerstore.New(driver.GetDB(), b, l)
+
+		const nbTry = 100
+
+		for i := 0; i < nbTry; i++ {
+			errChan := make(chan error, 2)
+
+			// Create a simple tx
+			tx1 := ledger.Transaction{
+				TransactionData: ledger.TransactionData{
+					Timestamp: now,
+					Reference: fmt.Sprintf("foo:%d", i),
+					Postings: []ledger.Posting{
+						ledger.NewPosting("world", "bank", "USD/2", big.NewInt(100)),
+					},
+				},
+			}
+			go func() {
+				errChan <- store.InsertTransaction(ctx, &tx1)
+			}()
+
+			// Create another tx with the same reference
+			tx2 := ledger.Transaction{
+				TransactionData: ledger.TransactionData{
+					Timestamp: now,
+					Reference: fmt.Sprintf("foo:%d", i),
+					Postings: []ledger.Posting{
+						ledger.NewPosting("world", "bank", "USD/2", big.NewInt(100)),
+					},
+				},
+			}
+			go func() {
+				errChan <- store.InsertTransaction(ctx, &tx2)
+			}()
+
+			select {
+			case err1 := <-errChan:
+				if err1 != nil {
+					require.True(t, errors.Is(err1, ledgercontroller.ErrTransactionReferenceConflict{}))
+					select {
+					case err2 := <-errChan:
+						require.NoError(t, err2)
+					case <-time.After(time.Second):
+						require.Fail(t, "should have received an error")
+					}
+				} else {
+					select {
+					case err2 := <-errChan:
+						require.Error(t, err2)
+						require.True(t, errors.Is(err2, ledgercontroller.ErrTransactionReferenceConflict{}))
+					case <-time.After(time.Second):
+						require.Fail(t, "should have received an error")
+					}
+				}
+			case <-time.After(time.Second):
+				require.Fail(t, "should have received an error")
+			}
+		}
+	})
 	t.Run("check denormalization", func(t *testing.T) {
 		t.Parallel()