diff --git a/Source/MQTTnet/Server/IMqttRetainedMessagesManager.cs b/Source/MQTTnet/Server/IMqttRetainedMessagesManager.cs
index 36ace613..6ffdd2bf 100644
--- a/Source/MQTTnet/Server/IMqttRetainedMessagesManager.cs
+++ b/Source/MQTTnet/Server/IMqttRetainedMessagesManager.cs
@@ -16,6 +16,6 @@ namespace MQTTnet.Server
 
         Task<IList<MqttApplicationMessage>> GetMessagesAsync();
 
-        Task<List<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters);
+        Task<IList<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters);
     }
 }
diff --git a/Source/MQTTnet/Server/MqttRetainedMessagesManager.cs b/Source/MQTTnet/Server/MqttRetainedMessagesManager.cs
index e79bcef8..c4e2f966 100644
--- a/Source/MQTTnet/Server/MqttRetainedMessagesManager.cs
+++ b/Source/MQTTnet/Server/MqttRetainedMessagesManager.cs
@@ -104,7 +104,7 @@ namespace MQTTnet.Server
             }
         }
 
-        public async Task<List<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters)
+        public async Task<IList<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters)
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));