diff --git a/lib/diaspora_federation/entities/conversation.rb b/lib/diaspora_federation/entities/conversation.rb
index 941d4d3..4b450f2 100644
--- a/lib/diaspora_federation/entities/conversation.rb
+++ b/lib/diaspora_federation/entities/conversation.rb
@@ -32,6 +32,15 @@ module DiasporaFederation
       #   The diaspora IDs of the persons participating the conversation separated by ";".
       #   @return [String] participants diaspora IDs
       property :participants, xml_name: :participant_handles
+
+      private
+
+      def validate
+        super
+        messages.each do |message|
+          raise ValidationError, "nested message has different author" if message.author != author
+        end
+      end
     end
   end
 end
diff --git a/spec/lib/diaspora_federation/entities/conversation_spec.rb b/spec/lib/diaspora_federation/entities/conversation_spec.rb
index 0bcb251..341ea37 100644
--- a/spec/lib/diaspora_federation/entities/conversation_spec.rb
+++ b/spec/lib/diaspora_federation/entities/conversation_spec.rb
@@ -3,11 +3,11 @@ module DiasporaFederation
     let(:parent) { FactoryGirl.create(:conversation, author: bob) }
     let(:parent_entity) { FactoryGirl.build(:related_entity, author: bob.diaspora_id) }
     let(:signed_msg1) {
-      FactoryGirl.build(:message_entity, author: alice.diaspora_id, parent_guid: parent.guid, parent: parent_entity)
+      FactoryGirl.build(:message_entity, author: bob.diaspora_id, parent_guid: parent.guid, parent: parent_entity)
                  .send(:xml_elements).merge(parent: parent_entity)
     }
     let(:signed_msg2) {
-      FactoryGirl.build(:message_entity, author: alice.diaspora_id, parent_guid: parent.guid, parent: parent_entity)
+      FactoryGirl.build(:message_entity, author: bob.diaspora_id, parent_guid: parent.guid, parent: parent_entity)
                  .send(:xml_elements).merge(parent: parent_entity)
     }
     let(:data) {
@@ -55,5 +55,14 @@ XML
         expect(parsed_instance.messages).to eq([])
       end
     end
+
+    context "nested entities" do
+      it "validates that nested messages have the same author" do
+        invalid_data = data.merge(author: alice.diaspora_id)
+        expect {
+          Entities::Conversation.new(invalid_data)
+        }.to raise_error Entity::ValidationError, "nested message has different author"
+      end
+    end
   end
 end