diff --git a/server/message_cache.go b/server/message_cache.go
index 03cb4969..64561d02 100644
--- a/server/message_cache.go
+++ b/server/message_cache.go
@@ -9,6 +9,7 @@ import (
 	"path/filepath"
 	"strings"
 	"time"
+	"sync"
 
 	_ "github.com/mattn/go-sqlite3" // SQLite driver
 	"heckel.io/ntfy/v2/log"
@@ -36,7 +37,7 @@ const (
 			priority INT NOT NULL,
 			tags TEXT NOT NULL,
 			click TEXT NOT NULL,
-			icon TEXT NOT NULL,			
+			icon TEXT NOT NULL,
 			actions TEXT NOT NULL,
 			attachment_name TEXT NOT NULL,
 			attachment_type TEXT NOT NULL,
@@ -73,30 +74,30 @@ const (
 	selectRowIDFromMessageID          = `SELECT id FROM messages WHERE mid = ?` // Do not include topic, see #336 and TestServer_PollSinceID_MultipleTopics
 	selectMessagesByIDQuery           = `
 		SELECT mid, time, expires, topic, message, title, priority, tags, click, icon, actions, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, sender, user, content_type, encoding
-		FROM messages 
+		FROM messages
 		WHERE mid = ?
 	`
 	selectMessagesSinceTimeQuery = `
 		SELECT mid, time, expires, topic, message, title, priority, tags, click, icon, actions, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, sender, user, content_type, encoding
-		FROM messages 
+		FROM messages
 		WHERE topic = ? AND time >= ? AND published = 1
 		ORDER BY time, id
 	`
 	selectMessagesSinceTimeIncludeScheduledQuery = `
 		SELECT mid, time, expires, topic, message, title, priority, tags, click, icon, actions, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, sender, user, content_type, encoding
-		FROM messages 
+		FROM messages
 		WHERE topic = ? AND time >= ?
 		ORDER BY time, id
 	`
 	selectMessagesSinceIDQuery = `
 		SELECT mid, time, expires, topic, message, title, priority, tags, click, icon, actions, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, sender, user, content_type, encoding
-		FROM messages 
+		FROM messages
 		WHERE topic = ? AND id > ? AND published = 1 
 		ORDER BY time, id
 	`
 	selectMessagesSinceIDIncludeScheduledQuery = `
 		SELECT mid, time, expires, topic, message, title, priority, tags, click, icon, actions, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, sender, user, content_type, encoding
-		FROM messages 
+		FROM messages
 		WHERE topic = ? AND (id > ? OR published = 0)
 		ORDER BY time, id
 	`
@@ -106,10 +107,10 @@ const (
 		WHERE topic = ? AND published = 1
 		ORDER BY time DESC, id DESC
 		LIMIT 1
-  `
+	`
 	selectMessagesDueQuery = `
 		SELECT mid, time, expires, topic, message, title, priority, tags, click, icon, actions, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, sender, user, content_type, encoding
-		FROM messages 
+		FROM messages
 		WHERE time <= ? AND published = 0
 		ORDER BY time, id
 	`
@@ -282,6 +283,7 @@ var (
 type messageCache struct {
 	db    *sql.DB
 	queue *util.BatchingQueue[*message]
+	mu    sync.Mutex
 	nop   bool
 }
 
@@ -347,6 +349,8 @@ func (c *messageCache) AddMessage(m *message) error {
 // addMessages synchronously stores a match of messages. If the database is locked, the transaction waits until
 // SQLite's busy_timeout is exceeded before erroring out.
 func (c *messageCache) addMessages(ms []*message) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 	if c.nop {
 		return nil
 	}
@@ -528,6 +532,8 @@ func (c *messageCache) Message(id string) (*message, error) {
 }
 
 func (c *messageCache) MarkPublished(m *message) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 	_, err := c.db.Exec(updateMessagePublishedQuery, m.ID)
 	return err
 }
@@ -573,6 +579,8 @@ func (c *messageCache) Topics() (map[string]*topic, error) {
 }
 
 func (c *messageCache) DeleteMessages(ids ...string) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 	tx, err := c.db.Begin()
 	if err != nil {
 		return err
@@ -587,6 +595,8 @@ func (c *messageCache) DeleteMessages(ids ...string) error {
 }
 
 func (c *messageCache) ExpireMessages(topics ...string) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 	tx, err := c.db.Begin()
 	if err != nil {
 		return err
@@ -621,6 +631,8 @@ func (c *messageCache) AttachmentsExpired() ([]string, error) {
 }
 
 func (c *messageCache) MarkAttachmentsDeleted(ids ...string) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 	tx, err := c.db.Begin()
 	if err != nil {
 		return err
@@ -766,6 +778,8 @@ func readMessage(rows *sql.Rows) (*message, error) {
 }
 
 func (c *messageCache) UpdateStats(messages int64) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 	_, err := c.db.Exec(updateStatsQuery, messages)
 	return err
 }