diff --git a/SlackAPI/Conversation.cs b/SlackAPI/Conversation.cs
index def8d1a..4f7d46e 100644
--- a/SlackAPI/Conversation.cs
+++ b/SlackAPI/Conversation.cs
@@ -8,6 +8,14 @@ namespace SlackAPI
 {
     public class Conversation
     {
+        public enum Type
+        {
+            public_channel,
+            private_channel,
+            mpim,
+            im
+        }
+
         public string id;
         public DateTime created;
         public DateTime last_read;
@@ -16,4 +24,4 @@ public class Conversation
         public int unread_count;
         public Message latest;
     }
-}
+}
\ No newline at end of file
diff --git a/SlackAPI/SlackClient.cs b/SlackAPI/SlackClient.cs
index eae7033..ae97c31 100644
--- a/SlackAPI/SlackClient.cs
+++ b/SlackAPI/SlackClient.cs
@@ -147,7 +147,7 @@ public void ChannelsInvite(Action<ChannelInviteResponse> callback, string userId
             APIRequestWithToken(callback, parameters.ToArray());
         }
 
-        public void GetConversationsList(Action<ConversationsListResponse> callback, string cursor = "", bool ExcludeArchived = true, int limit = 100, string[] types = null)
+        public void GetConversationsList(Action<ConversationsListResponse> callback, string cursor = "", bool ExcludeArchived = true, int limit = 100, Conversation.Type[] types = null)
         {
 	        List<Tuple<string, string>> parameters = new List<Tuple<string, string>>()
 	        {
@@ -155,7 +155,7 @@ public void GetConversationsList(Action<ConversationsListResponse> callback, str
 	        };
 	        if (limit > 0)
 		        parameters.Add(Tuple.Create("limit", limit.ToString())); 
-	        if (types.Any())
+	        if (types != null && types.Any())
 		        parameters.Add(Tuple.Create("types", string.Join(",", types)));
 	        if (!string.IsNullOrEmpty(cursor))
 		        parameters.Add(Tuple.Create("cursor", cursor));
diff --git a/SlackAPI/SlackTaskClient.cs b/SlackAPI/SlackTaskClient.cs
index c6815d2..f66abcf 100644
--- a/SlackAPI/SlackTaskClient.cs
+++ b/SlackAPI/SlackTaskClient.cs
@@ -127,7 +127,7 @@ public Task<ChannelInviteResponse> ChannelsInviteAsync(string userId, string cha
             return APIRequestWithTokenAsync<ChannelInviteResponse>(parameters.ToArray());
         }
 
-        public Task<ConversationsListResponse> GetConversationsListAsync(string cursor = "", bool ExcludeArchived = true, int limit = 100, string[] types = null)
+        public Task<ConversationsListResponse> GetConversationsListAsync(string cursor = "", bool ExcludeArchived = true, int limit = 100, Conversation.Type[] types = null)
         {
 	        List<Tuple<string, string>> parameters = new List<Tuple<string, string>>()
 	        {