diff --git a/pkg/services/ngalert/notifier/redis_peer.go b/pkg/services/ngalert/notifier/redis_peer.go
index 4419c4d8d8c..a75a2e8ce5a 100644
--- a/pkg/services/ngalert/notifier/redis_peer.go
+++ b/pkg/services/ngalert/notifier/redis_peer.go
@@ -13,6 +13,7 @@ import (
 	"github.com/prometheus/alertmanager/cluster"
 	"github.com/prometheus/alertmanager/cluster/clusterpb"
 	"github.com/prometheus/client_golang/prometheus"
+	"golang.org/x/exp/slices"
 
 	"github.com/redis/go-redis/v9"
 
@@ -239,11 +240,7 @@ func (p *redisPeer) membersSyncLoop() {
 
 func (p *redisPeer) membersSync() {
 	startTime := time.Now()
-	// The 100 is a hint for the server, how many records there might be for the
-	// provided pattern. It _might_ only return the first 100 records, which should
-	// be more than enough for our use case.
-	// More here: https://redis.io/commands/scan/
-	members, _, err := p.redis.Scan(context.Background(), 0, p.withPrefix(peerPattern), 100).Result()
+	members, err := p.membersScan()
 	if err != nil {
 		p.logger.Error("error getting keys from redis", "err", err, "pattern", p.withPrefix(peerPattern))
 		// To prevent a spike of duplicate messages, we return for the duration of
@@ -273,6 +270,11 @@ func (p *redisPeer) membersSync() {
 	// those out that have failed to send a heartbeat during the heartbeatTimeout.
 	peers := p.filterUnhealthyMembers(members, values.Val())
 	sort.Strings(peers)
+
+	// Redis Scan may return duplicate elements
+	// Filtering duplicates with Compact after sorting to prevent inconsistencies when calculating Position
+	peers = slices.Compact(peers)
+
 	dur := time.Since(startTime)
 	p.logger.Debug("membership sync done", "duration_ms", dur.Milliseconds())
 	p.membersMtx.Lock()
@@ -281,6 +283,30 @@ func (p *redisPeer) membersSync() {
 	p.membersFetchedAt = time.Now()
 }
 
+func (p *redisPeer) membersScan() ([]string, error) {
+	var (
+		cursor  uint64
+		err     error
+		members = []string{}
+		keys    []string
+	)
+	// The 100 is a hint for the server, how many records there might be for the
+	// provided pattern. It _might_ only return the first 100 records, which should
+	// be more than enough for our use case.
+	// More here: https://redis.io/commands/scan/
+	for {
+		keys, cursor, err = p.redis.Scan(context.Background(), cursor, p.withPrefix(peerPattern), 100).Result()
+		if err != nil {
+			return []string{}, err
+		}
+		members = append(members, keys...)
+		if cursor == 0 {
+			break
+		}
+	}
+	return members, nil
+}
+
 // filterUnhealthyMembers will filter out the members that have failed to send
 // a heartbeat since heartbeatTimeout.
 func (p *redisPeer) filterUnhealthyMembers(members []string, values []interface{}) []string {
@@ -318,12 +344,11 @@ func (p *redisPeer) Position() int {
 // Returns the known size of the Cluster. This also includes dead nodes that
 // haven't timeout yet.
 func (p *redisPeer) ClusterSize() int {
-	scan := p.redis.Scan(context.Background(), 0, p.withPrefix(peerPattern), 100)
-	if scan.Err() != nil {
-		p.logger.Error("error getting keys from redis", "err", scan.Err(), "pattern", p.withPrefix(peerPattern))
+	members, err := p.membersScan()
+	if err != nil {
+		p.logger.Error("error getting keys from redis", "err", err, "pattern", p.withPrefix(peerPattern))
 		return 0
 	}
-	members, _ := scan.Val()
 	return len(members)
 }