diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/tasks/SendToDeviceTask.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/tasks/SendToDeviceTask.kt
index 4b60d54238..c6af9b0cd1 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/tasks/SendToDeviceTask.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/tasks/SendToDeviceTask.kt
@@ -46,7 +46,9 @@ internal class DefaultSendToDeviceTask @Inject constructor(
                 messages = params.contentMap.map
         )
 
-        // Create a unique txnId first, to use the same value if the request is retried
+        // If params.transactionId is not provided, we create a unique txnId.
+        // It's important to do that outside the requestBlock parameter of executeRequest()
+        // to use the same value if the request is retried
         val txnId = params.transactionId ?: createUniqueTxnId()
 
         return executeRequest(
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/util/RequestIdHelper.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/util/RequestIdHelper.kt
index 9b3cb1942a..3106d5820c 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/util/RequestIdHelper.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/util/RequestIdHelper.kt
@@ -19,5 +19,5 @@ package org.matrix.android.sdk.internal.crypto.util
 import java.util.UUID
 
 internal object RequestIdHelper {
-    fun createUniqueRequestId() = "req_" + UUID.randomUUID().toString()
+    fun createUniqueRequestId() = UUID.randomUUID().toString()
 }