diff --git a/app/serializers/topic_view_serializer.rb b/app/serializers/topic_view_serializer.rb
index a109ff34a..a616c4a1b 100644
--- a/app/serializers/topic_view_serializer.rb
+++ b/app/serializers/topic_view_serializer.rb
@@ -66,14 +66,17 @@ class TopicViewSerializer < ApplicationSerializer
     }
 
     if object.topic.private_message?
-      result[:allowed_users] = object.topic.allowed_users.map do |user|
-        BasicUserSerializer.new(user, scope: scope, root: false)
-      end
-    end
+      allowed_user_ids = Set.new
 
-    if object.topic.private_message?
-      result[:allowed_groups] = object.topic.allowed_groups.map do |ag|
-        BasicGroupSerializer.new(ag, scope: scope, root: false)
+      result[:allowed_groups] = object.topic.allowed_groups.map do |group|
+        allowed_user_ids.merge(GroupUser.where(group: group).pluck(:user_id))
+        BasicGroupSerializer.new(group, scope: scope, root: false)
+      end
+
+      result[:allowed_users] = object.topic.allowed_users.select do |user|
+        !allowed_user_ids.include?(user.id)
+      end.map do |user|
+        BasicUserSerializer.new(user, scope: scope, root: false)
       end
     end
 
@@ -83,7 +86,6 @@ class TopicViewSerializer < ApplicationSerializer
       end
     end
 
-
     if object.suggested_topics.try(:topics).present?
       result[:suggested_topics] = object.suggested_topics.topics.map do |user|
         SuggestedTopicSerializer.new(user, scope: scope, root: false)