diff --git a/pkg/deploytest/simtimer.go b/pkg/deploytest/simtimer.go
index 415bd5966..726f9f80c 100644
--- a/pkg/deploytest/simtimer.go
+++ b/pkg/deploytest/simtimer.go
@@ -19,7 +19,7 @@ import (
 type simTimerModule struct {
 	*SimNode
 	eventsOut chan *events.EventList
-	processes map[t.TimerRetIndex]*testsim.Process
+	processes map[t.RetentionIndex]*testsim.Process
 }
 
 // NewSimTimerModule returns a Timer modules to be used in simulation.
@@ -27,7 +27,7 @@ func NewSimTimerModule(node *SimNode) modules.ActiveModule {
 	return &simTimerModule{
 		SimNode:   node,
 		eventsOut: make(chan *events.EventList, 1),
-		processes: map[t.TimerRetIndex]*testsim.Process{},
+		processes: map[t.RetentionIndex]*testsim.Process{},
 	}
 }
 
@@ -55,10 +55,10 @@ func (m *simTimerModule) applyEvent(ctx context.Context, e *eventpb.Event) error
 	case *eventpb.Event_TimerRepeat:
 		eventsOut := events.EmptyList().PushBackSlice(e.TimerRepeat.Events)
 		d := t.TimeDuration(e.TimerRepeat.Delay)
-		retIdx := t.TimerRetIndex(e.TimerRepeat.RetentionIndex)
+		retIdx := t.RetentionIndex(e.TimerRepeat.RetentionIndex)
 		m.repeat(ctx, eventsOut, d, retIdx)
 	case *eventpb.Event_TimerGarbageCollect:
-		retIdx := t.TimerRetIndex(e.TimerGarbageCollect.RetentionIndex)
+		retIdx := t.RetentionIndex(e.TimerGarbageCollect.RetentionIndex)
 		m.garbageCollect(retIdx)
 	default:
 		return fmt.Errorf("unexpected type of Timer event: %T", e)
@@ -99,7 +99,7 @@ func (m *simTimerModule) delay(ctx context.Context, eventList *events.EventList,
 	}()
 }
 
-func (m *simTimerModule) repeat(ctx context.Context, eventList *events.EventList, d t.TimeDuration, retIdx t.TimerRetIndex) {
+func (m *simTimerModule) repeat(ctx context.Context, eventList *events.EventList, d t.TimeDuration, retIdx t.RetentionIndex) {
 	proc := m.Spawn()
 	m.processes[retIdx] = proc
 
@@ -132,7 +132,7 @@ func (m *simTimerModule) repeat(ctx context.Context, eventList *events.EventList
 	}()
 }
 
-func (m *simTimerModule) garbageCollect(retIdx t.TimerRetIndex) {
+func (m *simTimerModule) garbageCollect(retIdx t.RetentionIndex) {
 	for i, proc := range m.processes {
 		if i < retIdx {
 			proc.Kill()
diff --git a/pkg/events/events.go b/pkg/events/events.go
index 00f9b5abe..db959398e 100644
--- a/pkg/events/events.go
+++ b/pkg/events/events.go
@@ -236,7 +236,7 @@ func NodeSigsVerified(
 
 // WALAppend returns an event of appending a new entry to the WAL.
 // This event is produced by the protocol state machine for persisting its state.
-func WALAppend(destModule t.ModuleID, event *eventpb.Event, retentionIndex t.WALRetIndex) *eventpb.Event {
+func WALAppend(destModule t.ModuleID, event *eventpb.Event, retentionIndex t.RetentionIndex) *eventpb.Event {
 	return &eventpb.Event{DestModule: destModule.Pb(), Type: &eventpb.Event_WalAppend{WalAppend: &eventpb.WALAppend{
 		Event:          event,
 		RetentionIndex: retentionIndex.Pb(),
@@ -246,7 +246,7 @@ func WALAppend(destModule t.ModuleID, event *eventpb.Event, retentionIndex t.WAL
 // WALTruncate returns and event on removing all entries from the WAL
 // that have been appended with a retentionIndex smaller than the
 // specified one.
-func WALTruncate(destModule t.ModuleID, retentionIndex t.WALRetIndex) *eventpb.Event {
+func WALTruncate(destModule t.ModuleID, retentionIndex t.RetentionIndex) *eventpb.Event {
 	return &eventpb.Event{
 		DestModule: destModule.Pb(),
 		Type: &eventpb.Event_WalTruncate{WalTruncate: &eventpb.WALTruncate{
@@ -257,7 +257,7 @@ func WALTruncate(destModule t.ModuleID, retentionIndex t.WALRetIndex) *eventpb.E
 
 // WALEntry returns an event of reading an entry from the WAL.
 // Those events are used at system initialization.
-func WALEntry(persistedEvent *eventpb.Event, retentionIndex t.WALRetIndex) *eventpb.Event {
+func WALEntry(persistedEvent *eventpb.Event, retentionIndex t.RetentionIndex) *eventpb.Event {
 	return &eventpb.Event{Type: &eventpb.Event_WalEntry{WalEntry: &eventpb.WALEntry{
 		Event: persistedEvent,
 	}}}
@@ -339,7 +339,7 @@ func TimerRepeat(
 	destModule t.ModuleID,
 	events []*eventpb.Event,
 	delay t.TimeDuration,
-	retIndex t.TimerRetIndex,
+	retIndex t.RetentionIndex,
 ) *eventpb.Event {
 	return &eventpb.Event{
 		DestModule: destModule.Pb(),
@@ -351,7 +351,7 @@ func TimerRepeat(
 	}
 }
 
-func TimerGarbageCollect(destModule t.ModuleID, retIndex t.TimerRetIndex) *eventpb.Event {
+func TimerGarbageCollect(destModule t.ModuleID, retIndex t.RetentionIndex) *eventpb.Event {
 	return &eventpb.Event{
 		DestModule: destModule.Pb(),
 		Type: &eventpb.Event_TimerGarbageCollect{TimerGarbageCollect: &eventpb.TimerGarbageCollect{
diff --git a/pkg/iss/checkpoint.go b/pkg/iss/checkpoint.go
index fb48a5e5a..ec759c111 100644
--- a/pkg/iss/checkpoint.go
+++ b/pkg/iss/checkpoint.go
@@ -138,7 +138,7 @@ func (ct *checkpointTracker) ProcessCheckpointSignResult(signature []byte) *even
 
 	// Write Checkpoint to WAL
 	persistEvent := PersistCheckpointEvent(ct.seqNr, ct.stateSnapshot, ct.stateSnapshotHash, signature)
-	walEvent := events.WALAppend(walModuleName, persistEvent, t.WALRetIndex(ct.epoch))
+	walEvent := events.WALAppend(walModuleName, persistEvent, t.RetentionIndex(ct.epoch))
 
 	// Send a checkpoint message to all nodes after persisting checkpoint to the WAL.
 	m := CheckpointMessage(ct.epoch, ct.seqNr, ct.stateSnapshotHash, signature)
@@ -146,7 +146,7 @@ func (ct *checkpointTracker) ProcessCheckpointSignResult(signature []byte) *even
 		"timer",
 		[]*eventpb.Event{events.SendMessage(netModuleName, m, ct.membership)},
 		ct.resendPeriod,
-		t.TimerRetIndex(ct.epoch)),
+		t.RetentionIndex(ct.epoch)),
 	)
 
 	ct.Log(logging.LevelDebug, "Sending checkpoint message",
@@ -247,7 +247,7 @@ func (ct *checkpointTracker) announceStable() *events.EventList {
 	persistEvent := events.WALAppend(
 		walModuleName,
 		PersistStableCheckpointEvent(stableCheckpoint),
-		t.WALRetIndex(ct.epoch),
+		t.RetentionIndex(ct.epoch),
 	)
 	persistEvent.FollowUp(StableCheckpointEvent(stableCheckpoint))
 	return events.ListOf(persistEvent)
diff --git a/pkg/iss/iss.go b/pkg/iss/iss.go
index cd358b7ab..ac22db4c4 100644
--- a/pkg/iss/iss.go
+++ b/pkg/iss/iss.go
@@ -641,8 +641,8 @@ func (iss *ISS) applyStableCheckpoint(stableCheckpoint *isspb.StableCheckpoint)
 		if pruneIndex > 0 { // "> 0" and not ">= 0", since only entries strictly smaller than the index are pruned.
 
 			// Prune WAL and Timer
-			eventsOut.PushBack(events.WALTruncate(walModuleName, t.WALRetIndex(pruneIndex)))
-			eventsOut.PushBack(events.TimerGarbageCollect(timerModuleName, t.TimerRetIndex(pruneIndex)))
+			eventsOut.PushBack(events.WALTruncate(walModuleName, t.RetentionIndex(pruneIndex)))
+			eventsOut.PushBack(events.TimerGarbageCollect(timerModuleName, t.RetentionIndex(pruneIndex)))
 
 			// Prune epoch state.
 			for epoch := range iss.epochs {
@@ -663,7 +663,7 @@ func (iss *ISS) applyStableCheckpoint(stableCheckpoint *isspb.StableCheckpoint)
 				// Note that we are not using the current epoch number here, because it is not relevant for checkpoints.
 				// Using pruneIndex makes sure that the re-transmission is stopped
 				// on every stable checkpoint (when another one is started).
-				t.TimerRetIndex(pruneIndex),
+				t.RetentionIndex(pruneIndex),
 			))
 
 		}
diff --git a/pkg/iss/sbeventservice.go b/pkg/iss/sbeventservice.go
index 6e817712a..d689390c9 100644
--- a/pkg/iss/sbeventservice.go
+++ b/pkg/iss/sbeventservice.go
@@ -46,7 +46,7 @@ func (ec *sbEventService) SendMessage(message *isspb.SBInstanceMessage, destinat
 // On recovery, this event will be fed back to the same orderer instance
 // (which, however, must be created during the recovery process).
 func (ec *sbEventService) WALAppend(event *isspb.SBInstanceEvent) *eventpb.Event {
-	return events.WALAppend(walModuleName, SBEvent(ec.epoch, ec.instance, event), t.WALRetIndex(ec.epoch))
+	return events.WALAppend(walModuleName, SBEvent(ec.epoch, ec.instance, event), t.RetentionIndex(ec.epoch))
 }
 
 func (ec *sbEventService) HashRequest(data [][][]byte, origin *isspb.SBInstanceHashOrigin) *eventpb.Event {
@@ -77,7 +77,7 @@ func (ec *sbEventService) TimerDelay(delay t.TimeDuration, evts ...*eventpb.Even
 }
 
 func (ec *sbEventService) TimerRepeat(period t.TimeDuration, evts ...*eventpb.Event) *eventpb.Event {
-	return events.TimerRepeat(timerModuleName, evts, period, t.TimerRetIndex(ec.epoch))
+	return events.TimerRepeat(timerModuleName, evts, period, t.RetentionIndex(ec.epoch))
 }
 
 // SBEvent creates an event to be processed by ISS in association with the orderer that created it (e.g. Deliver).
diff --git a/pkg/simplewal/simplewal.go b/pkg/simplewal/simplewal.go
index 5b8b7bf31..1eaaee4ce 100644
--- a/pkg/simplewal/simplewal.go
+++ b/pkg/simplewal/simplewal.go
@@ -42,14 +42,14 @@ type WAL struct {
 	// It is required to skip outdated entries when loading.
 	// Otherwise it could be completely ephemeral.
 	// TODO: Implement persisting and loading the retentionIndex
-	retentionIndex t.WALRetIndex
+	retentionIndex t.RetentionIndex
 }
 
 func (w *WAL) LoadAll(ctx context.Context) (*events.EventList, error) {
 	storedEvents := events.EmptyList()
 
 	// Add all events from the WAL to the new EventList.
-	if err := w.loadAll(func(retIdx t.WALRetIndex, event *eventpb.Event) {
+	if err := w.loadAll(func(retIdx t.RetentionIndex, event *eventpb.Event) {
 		storedEvents.PushBack(event)
 	}); err != nil {
 		return nil, fmt.Errorf("could not load WAL events: %w", err)
@@ -69,12 +69,12 @@ func (w *WAL) ApplyEvent(event *eventpb.Event) (*events.EventList, error) {
 	case *eventpb.Event_Init:
 		// no actions on init
 	case *eventpb.Event_WalAppend:
-		if err := w.Append(e.WalAppend.Event, t.WALRetIndex(e.WalAppend.RetentionIndex)); err != nil {
+		if err := w.Append(e.WalAppend.Event, t.RetentionIndex(e.WalAppend.RetentionIndex)); err != nil {
 			return nil, fmt.Errorf("could not persist event (retention index %d) to WAL: %w",
 				e.WalAppend.RetentionIndex, err)
 		}
 	case *eventpb.Event_WalTruncate:
-		if err := w.Truncate(t.WALRetIndex(e.WalTruncate.RetentionIndex)); err != nil {
+		if err := w.Truncate(t.RetentionIndex(e.WalTruncate.RetentionIndex)); err != nil {
 			return nil, fmt.Errorf("could not truncate WAL (retention index %d): %w",
 				e.WalTruncate.RetentionIndex, err)
 		}
@@ -130,7 +130,7 @@ func (w *WAL) IsEmpty() (bool, error) {
 	return firstIndex == 0, nil
 }
 
-func (w *WAL) loadAll(forEach func(index t.WALRetIndex, p *eventpb.Event)) error {
+func (w *WAL) loadAll(forEach func(index t.RetentionIndex, p *eventpb.Event)) error {
 	w.mutex.Lock()
 	defer w.mutex.Unlock()
 	firstIndex, err := w.log.FirstIndex()
@@ -160,8 +160,8 @@ func (w *WAL) loadAll(forEach func(index t.WALRetIndex, p *eventpb.Event)) error
 			return errors.WithMessage(err, "error decoding to proto, is the WAL corrupt?")
 		}
 
-		if t.WALRetIndex(result.RetentionIndex) >= w.retentionIndex {
-			forEach(t.WALRetIndex(result.RetentionIndex), result.Event)
+		if t.RetentionIndex(result.RetentionIndex) >= w.retentionIndex {
+			forEach(t.RetentionIndex(result.RetentionIndex), result.Event)
 		}
 	}
 
@@ -187,14 +187,14 @@ func (w *WAL) write(index uint64, entry *WALEntry) error {
 	return w.log.Write(index+1, data) // The log implementation seems to be indexing starting with 1.
 }
 
-func (w *WAL) Append(event *eventpb.Event, retentionIndex t.WALRetIndex) error {
+func (w *WAL) Append(event *eventpb.Event, retentionIndex t.RetentionIndex) error {
 	return w.write(w.idx, &WALEntry{
 		RetentionIndex: retentionIndex.Pb(),
 		Event:          event,
 	})
 }
 
-func (w *WAL) Truncate(retentionIndex t.WALRetIndex) error {
+func (w *WAL) Truncate(retentionIndex t.RetentionIndex) error {
 	w.mutex.Lock()
 	defer w.mutex.Unlock()
 
diff --git a/pkg/timer/timer.go b/pkg/timer/timer.go
index d2da68448..f3f29c92e 100644
--- a/pkg/timer/timer.go
+++ b/pkg/timer/timer.go
@@ -17,7 +17,7 @@ type Timer struct {
 	eventsOut chan *events.EventList
 
 	retIndexMutex sync.RWMutex
-	retIndex      t.TimerRetIndex
+	retIndex      t.RetentionIndex
 }
 
 func New() *Timer {
@@ -55,10 +55,10 @@ func (tm *Timer) ApplyEvents(ctx context.Context, eventList *events.EventList) e
 				ctx,
 				events.EmptyList().PushBackSlice(e.TimerRepeat.Events),
 				t.TimeDuration(e.TimerRepeat.Delay),
-				t.TimerRetIndex(e.TimerRepeat.RetentionIndex),
+				t.RetentionIndex(e.TimerRepeat.RetentionIndex),
 			)
 		case *eventpb.Event_TimerGarbageCollect:
-			tm.GarbageCollect(t.TimerRetIndex(e.TimerGarbageCollect.RetentionIndex))
+			tm.GarbageCollect(t.RetentionIndex(e.TimerGarbageCollect.RetentionIndex))
 		default:
 			return fmt.Errorf("unexpected type of Timer event: %T", event.Type)
 		}
@@ -103,7 +103,7 @@ func (tm *Timer) Repeat(
 	ctx context.Context,
 	events *events.EventList,
 	period t.TimeDuration,
-	retIndex t.TimerRetIndex,
+	retIndex t.RetentionIndex,
 ) {
 	go func() {
 
@@ -139,7 +139,7 @@ func (tm *Timer) Repeat(
 // When GarbageCollect is called, the Timer stops repeatedly producing events associated with a retention index
 // smaller than retIndex.
 // If GarbageCollect already has been invoked with the same or higher retention index, the call has no effect.
-func (tm *Timer) GarbageCollect(retIndex t.TimerRetIndex) {
+func (tm *Timer) GarbageCollect(retIndex t.RetentionIndex) {
 	tm.retIndexMutex.Lock()
 	defer tm.retIndexMutex.Unlock()
 
@@ -149,7 +149,7 @@ func (tm *Timer) GarbageCollect(retIndex t.TimerRetIndex) {
 	}
 }
 
-func (tm *Timer) getRetIndex() t.TimerRetIndex {
+func (tm *Timer) getRetIndex() t.RetentionIndex {
 	tm.retIndexMutex.RLock()
 	defer tm.retIndexMutex.RUnlock()
 
diff --git a/pkg/types/types.go b/pkg/types/types.go
index 803ee4537..3962fd64c 100644
--- a/pkg/types/types.go
+++ b/pkg/types/types.go
@@ -226,22 +226,12 @@ func (rn ReqNo) Pb() uint64 {
 
 // ================================================================================
 
-// WALRetIndex represents the WAL (Write-Ahead Log) retention index assigned to every entry (and used for truncating).
-type WALRetIndex uint64
+// RetentionIndex represents the WAL (Write-Ahead Log) retention index assigned to every entry (and used for truncating).
+type RetentionIndex uint64
 
-// Pb converts a WALRetIndex to its underlying native type.
-func (wri WALRetIndex) Pb() uint64 {
-	return uint64(wri)
-}
-
-// ================================================================================
-
-// TimerRetIndex represents the Timer retention index used for garbage-collecting "Repeat" invocations.
-type TimerRetIndex uint64
-
-// Pb converts a TimerRetIndex to its underlying native type.
-func (tri TimerRetIndex) Pb() uint64 {
-	return uint64(tri)
+// Pb converts a RetentionIndex to its underlying native type.
+func (ri RetentionIndex) Pb() uint64 {
+	return uint64(ri)
 }
 
 // ================================================================================