diff --git a/.changeset/idempotent-add-simulcast-track.md b/.changeset/idempotent-add-simulcast-track.md
new file mode 100644
index 000000000..6a429e994
--- /dev/null
+++ b/.changeset/idempotent-add-simulcast-track.md
@@ -0,0 +1,5 @@
+---
+"client-sdk-android": patch
+---
+
+Fix crash when a duplicate SubscribedQualityUpdate requests a backup codec that is already added. addSimulcastTrack now skips the duplicate instead of throwing IllegalStateException ("VP8 already added!"), matching the JS SDK behavior.
diff --git a/livekit-android-sdk/src/main/java/io/livekit/android/room/participant/LocalParticipant.kt b/livekit-android-sdk/src/main/java/io/livekit/android/room/participant/LocalParticipant.kt
index 75ac69c11..619a540c8 100644
--- a/livekit-android-sdk/src/main/java/io/livekit/android/room/participant/LocalParticipant.kt
+++ b/livekit-android-sdk/src/main/java/io/livekit/android/room/participant/LocalParticipant.kt
@@ -1273,7 +1273,10 @@ internal constructor(
             return
         }
         val (newOptions, newEncodings) = result
-        val simulcastTrack = track.addSimulcastTrack(codec, newEncodings)
+        // A duplicate SubscribedQualityUpdate can request a codec that is already being
+        // published (or mid-publish, before the sender is attached). Treat it as a no-op
+        // instead of throwing, so a repeated update doesn't crash the session.
+        val simulcastTrack = track.addSimulcastTrack(codec, newEncodings) ?: return
 
         val transceiverInit = RtpTransceiverInit(
             RtpTransceiver.RtpTransceiverDirection.SEND_ONLY,
diff --git a/livekit-android-sdk/src/main/java/io/livekit/android/room/track/LocalVideoTrack.kt b/livekit-android-sdk/src/main/java/io/livekit/android/room/track/LocalVideoTrack.kt
index 358ed6fb9..074e2ce08 100644
--- a/livekit-android-sdk/src/main/java/io/livekit/android/room/track/LocalVideoTrack.kt
+++ b/livekit-android-sdk/src/main/java/io/livekit/android/room/track/LocalVideoTrack.kt
@@ -430,9 +430,10 @@ constructor(
         return newCodecs
     }
 
-    internal fun addSimulcastTrack(codec: VideoCodec, encodings: List<RtpParameters.Encoding>): SimulcastTrackInfo {
+    internal fun addSimulcastTrack(codec: VideoCodec, encodings: List<RtpParameters.Encoding>): SimulcastTrackInfo? {
         if (this.simulcastCodecs.containsKey(codec)) {
-            throw IllegalStateException("$codec already added!")
+            LKLog.w { "$codec already added, skipping." }
+            return null
         }
         val simulcastTrackInfo = SimulcastTrackInfo(
             codec = codec.codecName,
diff --git a/livekit-android-test/src/test/java/io/livekit/android/room/participant/LocalParticipantMockE2ETest.kt b/livekit-android-test/src/test/java/io/livekit/android/room/participant/LocalParticipantMockE2ETest.kt
index 0498b8ed1..43869ea83 100644
--- a/livekit-android-test/src/test/java/io/livekit/android/room/participant/LocalParticipantMockE2ETest.kt
+++ b/livekit-android-test/src/test/java/io/livekit/android/room/participant/LocalParticipantMockE2ETest.kt
@@ -340,6 +340,36 @@ class LocalParticipantMockE2ETest : MockE2ETest() {
         assertEquals(4, getPublisherPeerConnection().transceivers.size)
     }
 
+    @Test
+    fun addSimulcastTrackForAlreadyAddedCodecIsNoOp() = runTest {
+        val videoTrack = createLocalTrack()
+
+        val first = videoTrack.addSimulcastTrack(VideoCodec.VP8, emptyList())
+        val second = videoTrack.addSimulcastTrack(VideoCodec.VP8, emptyList())
+
+        assertNotNull(first)
+        assertNull(second)
+    }
+
+    @Test
+    fun duplicateSubscribedQualityUpdateDoesNotRepublishBackupCodec() = runTest {
+        room.videoTrackPublishDefaults = room.videoTrackPublishDefaults.copy(
+            videoCodec = VideoCodec.VP9.codecName,
+            scalabilityMode = "L3T3",
+            backupCodec = BackupVideoCodec(codec = VideoCodec.VP8.codecName),
+        )
+
+        connect()
+        val videoTrack = createLocalTrack()
+        room.localParticipant.publishVideoTrack(videoTrack)
+
+        val trackSid = room.localParticipant.videoTrackPublications.first().first.sid
+        receiveSubscribedQualityUpdate(trackSid)
+        receiveSubscribedQualityUpdate(trackSid)
+
+        assertEquals(2, getPublisherPeerConnection().transceivers.size)
+    }
+
     @Test
     fun disposeDisposesVideoSource() {
         val source = mock(VideoSource::class.java)