diff --git a/app/src/main/java/io/heckel/ntfy/msg/ApiService.kt b/app/src/main/java/io/heckel/ntfy/msg/ApiService.kt
index f2ef456b..c7aaa6a7 100644
--- a/app/src/main/java/io/heckel/ntfy/msg/ApiService.kt
+++ b/app/src/main/java/io/heckel/ntfy/msg/ApiService.kt
@@ -16,7 +16,6 @@ import java.io.IOException
 import java.net.URLEncoder
 import java.nio.charset.StandardCharsets.UTF_8
 import java.util.concurrent.TimeUnit
-import kotlin.random.Random
 
 class ApiService(context: Context) {
     private val repository = Repository.getInstance(context)
@@ -139,7 +138,7 @@ class ApiService(context: Context) {
             val body = response.body.string().trim()
             if (body.isEmpty()) return emptyList()
             val notifications = body.lines().mapNotNull { line ->
-                parser.parse(line, subscriptionId = subscriptionId, notificationId = 0) // No notification when we poll
+                parser.parse(line, subscriptionId = subscriptionId) // No notification when we poll
             }
 
             Log.d(TAG, "Notifications: $notifications")
@@ -170,7 +169,7 @@ class ApiService(context: Context) {
                     val source = response.body.source()
                     while (!source.exhausted()) {
                         val line = source.readUtf8Line() ?: throw Exception("Unexpected response for $url: line is null")
-                        val notification = parser.parseWithTopic(line, notificationId = Random.nextInt(), subscriptionId = 0) // subscriptionId to be set downstream
+                        val notification = parser.parseWithTopic(line, notify = true, subscriptionId = 0) // subscriptionId to be set downstream
                         if (notification != null) {
                             notify(notification.topic, notification.notification)
                         }
diff --git a/app/src/main/java/io/heckel/ntfy/msg/NotificationParser.kt b/app/src/main/java/io/heckel/ntfy/msg/NotificationParser.kt
index 557c971d..95358034 100644
--- a/app/src/main/java/io/heckel/ntfy/msg/NotificationParser.kt
+++ b/app/src/main/java/io/heckel/ntfy/msg/NotificationParser.kt
@@ -6,6 +6,7 @@ import io.heckel.ntfy.db.Action
 import io.heckel.ntfy.db.Attachment
 import io.heckel.ntfy.db.Icon
 import io.heckel.ntfy.db.Notification
+import io.heckel.ntfy.util.deriveNotificationId
 import io.heckel.ntfy.util.joinTags
 import io.heckel.ntfy.util.toPriority
 import java.lang.reflect.Type
@@ -13,12 +14,12 @@ import java.lang.reflect.Type
 class NotificationParser {
     private val gson = Gson()
 
-    fun parse(s: String, subscriptionId: Long = 0, notificationId: Int = 0): Notification? {
-        val notificationWithTopic = parseWithTopic(s, subscriptionId = subscriptionId, notificationId = notificationId)
+    fun parse(s: String, subscriptionId: Long = 0, notify: Boolean = false): Notification? {
+        val notificationWithTopic = parseWithTopic(s, subscriptionId = subscriptionId, notify = notify)
         return notificationWithTopic?.notification
     }
 
-    fun parseWithTopic(s: String, subscriptionId: Long = 0, notificationId: Int = 0): NotificationWithTopic? {
+    fun parseWithTopic(s: String, subscriptionId: Long = 0, notify: Boolean = false): NotificationWithTopic? {
         val message = gson.fromJson(s, Message::class.java)
         if (message.event != ApiService.EVENT_MESSAGE) {
             return null
@@ -50,6 +51,8 @@ class NotificationParser {
         }
         val icon: Icon? = if (message.icon != null && message.icon != "") Icon(url = message.icon) else null
         val sid = message.sid ?: message.id // Default to id if sid not provided
+        // Derive notificationId from sid so updates replace the existing Android notification
+        val notificationId = if (notify) deriveNotificationId(sid) else 0
         val notification = Notification(
             id = message.id,
             subscriptionId = subscriptionId,
diff --git a/app/src/main/java/io/heckel/ntfy/service/WsConnection.kt b/app/src/main/java/io/heckel/ntfy/service/WsConnection.kt
index f72b6951..b119f5dd 100644
--- a/app/src/main/java/io/heckel/ntfy/service/WsConnection.kt
+++ b/app/src/main/java/io/heckel/ntfy/service/WsConnection.kt
@@ -16,7 +16,6 @@ import java.util.*
 import java.util.concurrent.TimeUnit
 import java.util.concurrent.atomic.AtomicLong
 import java.util.concurrent.atomic.AtomicReference
-import kotlin.random.Random
 
 /**
  * Connect to ntfy server via WebSockets. This connection represents a single connection to a server, with
@@ -148,7 +147,7 @@ class WsConnection(
         override fun onMessage(webSocket: WebSocket, text: String) {
             synchronize("onMessage") {
                 Log.d(TAG, "$shortUrl (gid=$globalId, lid=$id): Received message: $text")
-                val notificationWithTopic = parser.parseWithTopic(text, subscriptionId = 0, notificationId = Random.nextInt())
+                val notificationWithTopic = parser.parseWithTopic(text, subscriptionId = 0, notify = true)
                 if (notificationWithTopic == null) {
                     Log.d(TAG, "$shortUrl (gid=$globalId, lid=$id): Irrelevant or unknown message. Discarding.")
                     return@synchronize
diff --git a/app/src/main/java/io/heckel/ntfy/ui/MainActivity.kt b/app/src/main/java/io/heckel/ntfy/ui/MainActivity.kt
index f364e16c..2d2a7228 100644
--- a/app/src/main/java/io/heckel/ntfy/ui/MainActivity.kt
+++ b/app/src/main/java/io/heckel/ntfy/ui/MainActivity.kt
@@ -67,13 +67,13 @@ import io.heckel.ntfy.util.randomSubscriptionId
 import io.heckel.ntfy.util.shortUrl
 import io.heckel.ntfy.util.topicShortUrl
 import io.heckel.ntfy.work.DeleteWorker
+import io.heckel.ntfy.util.deriveNotificationId
 import io.heckel.ntfy.work.PollWorker
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
 import java.util.Date
 import java.util.concurrent.TimeUnit
-import kotlin.random.Random
 import androidx.core.view.size
 import androidx.core.view.get
 import androidx.core.net.toUri
@@ -709,7 +709,7 @@ class MainActivity : AppCompatActivity(), AddFragment.SubscribeListener, Notific
                     val newNotifications = repository.onlyNewNotifications(subscription.id, notifications)
                     newNotifications.forEach { notification ->
                         newNotificationsCount++
-                        val notificationWithId = notification.copy(notificationId = Random.nextInt())
+                        val notificationWithId = notification.copy(notificationId = deriveNotificationId(notification.sid))
                         if (repository.addNotification(notificationWithId)) {
                             dispatcher?.dispatch(subscription, notificationWithId)
                         }
diff --git a/app/src/main/java/io/heckel/ntfy/util/Util.kt b/app/src/main/java/io/heckel/ntfy/util/Util.kt
index 6d7ba987..70e6ee8c 100644
--- a/app/src/main/java/io/heckel/ntfy/util/Util.kt
+++ b/app/src/main/java/io/heckel/ntfy/util/Util.kt
@@ -503,3 +503,14 @@ fun Button.dangerButton() {
 fun Long.nullIfZero(): Long? {
     return if (this == 0L) return null else this
 }
+
+/**
+ * Derives a stable notification ID from a string (typically the sid or id).
+ * This allows Android to update existing notifications when a new version arrives.
+ * The result is always positive and never zero (0 means "no notification").
+ */
+fun deriveNotificationId(sid: String): Int {
+    val hash = sid.hashCode()
+    // Ensure the ID is positive and non-zero
+    return if (hash == 0 || hash == Int.MIN_VALUE) 1 else kotlin.math.abs(hash)
+}
diff --git a/app/src/main/java/io/heckel/ntfy/work/PollWorker.kt b/app/src/main/java/io/heckel/ntfy/work/PollWorker.kt
index cc431a32..e227745a 100644
--- a/app/src/main/java/io/heckel/ntfy/work/PollWorker.kt
+++ b/app/src/main/java/io/heckel/ntfy/work/PollWorker.kt
@@ -8,9 +8,9 @@ import io.heckel.ntfy.db.Repository
 import io.heckel.ntfy.msg.ApiService
 import io.heckel.ntfy.msg.NotificationDispatcher
 import io.heckel.ntfy.util.Log
+import io.heckel.ntfy.util.deriveNotificationId
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
-import kotlin.random.Random
 
 class PollWorker(ctx: Context, params: WorkerParameters) : CoroutineWorker(ctx, params) {
     // IMPORTANT:
@@ -49,7 +49,7 @@ class PollWorker(ctx: Context, params: WorkerParameters) : CoroutineWorker(ctx,
                     )
                     val newNotifications = repository
                         .onlyNewNotifications(subscription.id, notifications)
-                        .map { it.copy(notificationId = Random.nextInt()) }
+                        .map { it.copy(notificationId = deriveNotificationId(it.sid)) }
                     newNotifications.forEach { notification ->
                         if (repository.addNotification(notification)) {
                             dispatcher.dispatch(subscription, notification)
diff --git a/app/src/play/java/io/heckel/ntfy/firebase/FirebaseService.kt b/app/src/play/java/io/heckel/ntfy/firebase/FirebaseService.kt
index a348a063..47250481 100644
--- a/app/src/play/java/io/heckel/ntfy/firebase/FirebaseService.kt
+++ b/app/src/play/java/io/heckel/ntfy/firebase/FirebaseService.kt
@@ -14,6 +14,7 @@ import io.heckel.ntfy.msg.ApiService
 import io.heckel.ntfy.msg.NotificationDispatcher
 import io.heckel.ntfy.msg.NotificationParser
 import io.heckel.ntfy.service.SubscriberService
+import io.heckel.ntfy.util.deriveNotificationId
 import io.heckel.ntfy.util.nullIfZero
 import io.heckel.ntfy.util.toPriority
 import io.heckel.ntfy.util.topicShortUrl
@@ -21,7 +22,6 @@ import io.heckel.ntfy.work.PollWorker
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.launch
-import kotlin.random.Random
 
 class FirebaseService : FirebaseMessagingService() {
     private val repository by lazy { (application as Application).repository }
@@ -128,11 +128,12 @@ class FirebaseService : FirebaseMessagingService() {
                 )
             } else null
             val icon: Icon? = if (iconUrl != null && iconUrl != "") Icon(url = iconUrl) else null
+            val actualSid = sid ?: id
             val notification = Notification(
                 id = id,
                 subscriptionId = subscription.id,
                 timestamp = timestamp,
-                sid = sid ?: id,
+                sid = actualSid,
                 title = title ?: "",
                 message = message,
                 contentType = contentType ?: "",
@@ -143,7 +144,7 @@ class FirebaseService : FirebaseMessagingService() {
                 icon = icon,
                 actions = parser.parseActions(actions),
                 attachment = attachment,
-                notificationId = Random.nextInt(),
+                notificationId = deriveNotificationId(actualSid),
                 deleted = false
             )
             if (repository.addNotification(notification)) {