diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/SyncResponsePostTreatmentAggregator.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/SyncResponsePostTreatmentAggregator.kt
index 14f89e8a34..2e1863a034 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/SyncResponsePostTreatmentAggregator.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/SyncResponsePostTreatmentAggregator.kt
@@ -24,7 +24,7 @@ internal class SyncResponsePostTreatmentAggregator {
     val directChatsToCheck = mutableMapOf<String, String>()
 
     // List of userIds to fetch and update at the end of incremental syncs
-    val userIdsToFetch = mutableListOf<String>()
+    val userIdsToFetch = mutableSetOf<String>()
 
     // Set of users to call `crossSigningService.onUsersDeviceUpdate` once per sync
     val userIdsWithDeviceUpdate = mutableSetOf<String>()
diff --git a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/handler/SyncResponsePostTreatmentAggregatorHandler.kt b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/handler/SyncResponsePostTreatmentAggregatorHandler.kt
index fb7b7c60a0..b7806d154b 100644
--- a/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/handler/SyncResponsePostTreatmentAggregatorHandler.kt
+++ b/matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/sync/handler/SyncResponsePostTreatmentAggregatorHandler.kt
@@ -83,13 +83,13 @@ internal class SyncResponsePostTreatmentAggregatorHandler @Inject constructor(
         }
     }
 
-    private suspend fun fetchAndUpdateUsers(userIdsToFetch: List<String>) {
+    private suspend fun fetchAndUpdateUsers(userIdsToFetch: Collection<String>) {
         fetchUsers(userIdsToFetch)
                 .takeIf { it.isNotEmpty() }
                 ?.saveLocally()
     }
 
-    private suspend fun fetchUsers(userIdsToFetch: List<String>) = userIdsToFetch.mapNotNull {
+    private suspend fun fetchUsers(userIdsToFetch: Collection<String>) = userIdsToFetch.mapNotNull {
         tryOrNull {
             val profileJson = getProfileInfoTask.execute(GetProfileInfoTask.Params(it))
             User.fromJson(it, profileJson)