diff --git a/src/Discord.Net.Rest/Entities/Channels/ChannelHelper.cs b/src/Discord.Net.Rest/Entities/Channels/ChannelHelper.cs
index 1e3f27e60..aa90b2eee 100644
--- a/src/Discord.Net.Rest/Entities/Channels/ChannelHelper.cs
+++ b/src/Discord.Net.Rest/Entities/Channels/ChannelHelper.cs
@@ -172,6 +172,22 @@ namespace Discord.Rest
             Preconditions.AtMost(allowedMentions?.RoleIds?.Count ?? 0, 100, nameof(allowedMentions.RoleIds), "A max of 100 role Ids are allowed.");
             Preconditions.AtMost(allowedMentions?.UserIds?.Count ?? 0, 100, nameof(allowedMentions.UserIds), "A max of 100 user Ids are allowed.");
 
+            // check that user flag and user Id list are exclusive, same with role flag and role Id list
+            if (allowedMentions != null && allowedMentions.AllowedTypes.HasValue)
+            {
+                if (allowedMentions.AllowedTypes.Value.HasFlag(AllowedMentionTypes.Users) &&
+                    allowedMentions.UserIds != null && allowedMentions.UserIds.Count > 0)
+                {
+                    throw new ArgumentException("The Users flag is mutually exclusive with the list of User Ids.", nameof(allowedMentions));
+                }
+
+                if (allowedMentions.AllowedTypes.Value.HasFlag(AllowedMentionTypes.Roles) &&
+                    allowedMentions.RoleIds != null && allowedMentions.RoleIds.Count > 0)
+                {
+                    throw new ArgumentException("The Roles flag is mutually exclusive with the list of Role Ids.", nameof(allowedMentions));
+                }
+            }
+
             var args = new CreateMessageParams(text) { IsTTS = isTTS, Embed = embed?.ToModel(), AllowedMentions = allowedMentions?.ToModel() };
             var model = await client.ApiClient.CreateMessageAsync(channel.Id, args, options).ConfigureAwait(false);
             return RestUserMessage.Create(client, channel, client.CurrentUser, model);