diff --git a/lib/src/utils/multilock.dart b/lib/src/utils/multilock.dart
index cc2973b8..035232ef 100644
--- a/lib/src/utils/multilock.dart
+++ b/lib/src/utils/multilock.dart
@@ -1,4 +1,3 @@
-// @dart=2.9
 /*
  *   Famedly Matrix SDK
  *   Copyright (C) 2019, 2020, 2021 Famedly GmbH
@@ -40,7 +39,7 @@ class MultiLock<T> {
         if (_completers[key] != null) {
           futures.add(() async {
             while (_completers[key] != null) {
-              await _completers[key].future;
+              await _completers[key]!.future;
             }
           }());
         }
@@ -60,7 +59,7 @@ class MultiLock<T> {
     // we just have to simply unlock all the completers
     for (final key in uniqueKeys) {
       if (_completers[key] != null) {
-        final completer = _completers[key];
+        final completer = _completers[key]!;
         _completers.remove(key);
         completer.complete();
       }