diff --git a/matrix-sdk-android/src/kotlinCrypto/java/org/matrix/android/sdk/internal/crypto/DefaultCryptoService.kt b/matrix-sdk-android/src/kotlinCrypto/java/org/matrix/android/sdk/internal/crypto/DefaultCryptoService.kt
index 66550c4f33..d0bd65e9bb 100755
--- a/matrix-sdk-android/src/kotlinCrypto/java/org/matrix/android/sdk/internal/crypto/DefaultCryptoService.kt
+++ b/matrix-sdk-android/src/kotlinCrypto/java/org/matrix/android/sdk/internal/crypto/DefaultCryptoService.kt
@@ -1033,7 +1033,8 @@ internal class DefaultCryptoService @Inject constructor(
     override suspend fun receiveSyncChanges(
             toDevice: ToDeviceSyncResponse?,
             deviceChanges: DeviceListResponse?,
-            keyCounts: DeviceOneTimeKeysCountSyncResponse?
+            keyCounts: DeviceOneTimeKeysCountSyncResponse?,
+            deviceUnusedFallbackKeyTypes: List<String>?
     ) {
         withContext(coroutineDispatchers.crypto) {
             deviceListManager.handleDeviceListsChanges(deviceChanges?.changed.orEmpty(), deviceChanges?.left.orEmpty())
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/crypto/CryptoService.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/crypto/CryptoService.kt
index 060ed85d04..3b308fff95 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/crypto/CryptoService.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/crypto/CryptoService.kt
@@ -222,7 +222,13 @@ interface CryptoService {
     fun start()
     suspend fun onSyncWillProcess(isInitialSync: Boolean)
     fun isStarted(): Boolean
-    suspend fun receiveSyncChanges(toDevice: ToDeviceSyncResponse?, deviceChanges: DeviceListResponse?, keyCounts: DeviceOneTimeKeysCountSyncResponse?)
+
+    suspend fun receiveSyncChanges(
+            toDevice: ToDeviceSyncResponse?,
+            deviceChanges: DeviceListResponse?,
+            keyCounts: DeviceOneTimeKeysCountSyncResponse?,
+            deviceUnusedFallbackKeyTypes: List<String>?)
+
     suspend fun onLiveEvent(roomId: String, event: Event, isInitialSync: Boolean, cryptoStoreAggregator: CryptoStoreAggregator?)
     suspend fun onStateEvent(roomId: String, event: Event, cryptoStoreAggregator: CryptoStoreAggregator?) {}
     suspend fun onSyncCompleted(syncResponse: SyncResponse, cryptoStoreAggregator: CryptoStoreAggregator)
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/sync/model/SyncResponse.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/sync/model/SyncResponse.kt
index 382d8a1740..3948acef65 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/sync/model/SyncResponse.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/sync/model/SyncResponse.kt
@@ -64,5 +64,12 @@ data class SyncResponse(
          * but that algorithm is not listed in device_unused_fallback_key_types, the client will upload a new key.
          */
         @Json(name = "org.matrix.msc2732.device_unused_fallback_key_types")
-        val deviceUnusedFallbackKeyTypes: List<String>? = null,
-)
+        val devDeviceUnusedFallbackKeyTypes: List<String>? = null,
+        @Json(name = "device_unused_fallback_key_types")
+        val stableDeviceUnusedFallbackKeyTypes: List<String>? = null,
+
+        ) {
+
+    @Transient
+    val deviceUnusedFallbackKeyTypes: List<String>? = stableDeviceUnusedFallbackKeyTypes ?: devDeviceUnusedFallbackKeyTypes
+}
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/model/rest/KeysUploadBody.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/model/rest/KeysUploadBody.kt
index 363dee9a8d..1d1fb3e1fe 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/model/rest/KeysUploadBody.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/model/rest/KeysUploadBody.kt
@@ -46,6 +46,6 @@ internal data class KeysUploadBody(
          * If the user had previously uploaded a fallback key for a given algorithm, it is replaced.
          * The server will only keep one fallback key per algorithm for each user.
          */
-        @Json(name = "org.matrix.msc2732.fallback_keys")
+        @Json(name = "fallback_keys")
         val fallbackKeys: JsonDict? = null
 )
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/SyncResponseHandler.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/SyncResponseHandler.kt
index 737a8fd9f0..3d0c816cb0 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/SyncResponseHandler.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/SyncResponseHandler.kt
@@ -183,7 +183,8 @@ internal class SyncResponseHandler @Inject constructor(
                 cryptoService.receiveSyncChanges(
                         syncResponse.toDevice,
                         syncResponse.deviceLists,
-                        syncResponse.deviceOneTimeKeysCount
+                        syncResponse.deviceOneTimeKeysCount,
+                        syncResponse.deviceUnusedFallbackKeyTypes
                 )
             }.also {
                 Timber.v("Finish handling toDevice in $it ms")
diff --git a/matrix-sdk-android/src/rustCrypto/java/org/matrix/android/sdk/internal/crypto/OlmMachine.kt b/matrix-sdk-android/src/rustCrypto/java/org/matrix/android/sdk/internal/crypto/OlmMachine.kt
index 4424bdccdc..838dbf30f7 100644
--- a/matrix-sdk-android/src/rustCrypto/java/org/matrix/android/sdk/internal/crypto/OlmMachine.kt
+++ b/matrix-sdk-android/src/rustCrypto/java/org/matrix/android/sdk/internal/crypto/OlmMachine.kt
@@ -263,7 +263,8 @@ internal class OlmMachine @Inject constructor(
     suspend fun receiveSyncChanges(
             toDevice: ToDeviceSyncResponse?,
             deviceChanges: DeviceListResponse?,
-            keyCounts: DeviceOneTimeKeysCountSyncResponse?
+            keyCounts: DeviceOneTimeKeysCountSyncResponse?,
+            deviceUnusedFallbackKeyTypes: List<String>?,
     ): ToDeviceSyncResponse {
         val response = withContext(coroutineDispatchers.io) {
             val counts: MutableMap<String, Int> = mutableMapOf()
@@ -282,9 +283,8 @@ internal class OlmMachine @Inject constructor(
                     .adapter(ToDeviceSyncResponse::class.java)
             val events = adapter.toJson(toDevice ?: ToDeviceSyncResponse())
 
-            // TODO once our sync response type parses the unused fallback key
             // field pass in the list of unused fallback keys here
-            val receiveSyncChanges = inner.receiveSyncChanges(events, devices, counts, unusedFallbackKeys = null)
+            val receiveSyncChanges = inner.receiveSyncChanges(events, devices, counts, deviceUnusedFallbackKeyTypes)
 
             val outAdapter = moshi.adapter<List<Event>>(
                     Types.newParameterizedType(
diff --git a/matrix-sdk-android/src/rustCrypto/java/org/matrix/android/sdk/internal/crypto/RustCryptoService.kt b/matrix-sdk-android/src/rustCrypto/java/org/matrix/android/sdk/internal/crypto/RustCryptoService.kt
index 140cbde3be..d168663a1b 100755
--- a/matrix-sdk-android/src/rustCrypto/java/org/matrix/android/sdk/internal/crypto/RustCryptoService.kt
+++ b/matrix-sdk-android/src/rustCrypto/java/org/matrix/android/sdk/internal/crypto/RustCryptoService.kt
@@ -605,10 +605,11 @@ internal class RustCryptoService @Inject constructor(
     override suspend fun receiveSyncChanges(
             toDevice: ToDeviceSyncResponse?,
             deviceChanges: DeviceListResponse?,
-            keyCounts: DeviceOneTimeKeysCountSyncResponse?
+            keyCounts: DeviceOneTimeKeysCountSyncResponse?,
+            deviceUnusedFallbackKeyTypes: List<String>?,
     ) {
         // Decrypt and handle our to-device events
-        val toDeviceEvents = this.olmMachine.receiveSyncChanges(toDevice, deviceChanges, keyCounts)
+        val toDeviceEvents = this.olmMachine.receiveSyncChanges(toDevice, deviceChanges, keyCounts, deviceUnusedFallbackKeyTypes)
 
         // Notify the our listeners about room keys so decryption is retried.
         toDeviceEvents.events.orEmpty().forEach { event ->