diff --git a/lib/diaspora_federation/entities/conversation.rb b/lib/diaspora_federation/entities/conversation.rb
index 9745ffb..6726dfd 100644
--- a/lib/diaspora_federation/entities/conversation.rb
+++ b/lib/diaspora_federation/entities/conversation.rb
@@ -4,6 +4,12 @@ module DiasporaFederation
     #
     # @see Validators::ConversationValidator
     class Conversation < Entity
+      # @!attribute [r] author
+      #   The diaspora* ID of the person initiated the conversation
+      #   @see Person#author
+      #   @return [String] diaspora* ID
+      property :author, xml_name: :diaspora_handle
+
       # @!attribute [r] guid
       #   A random string of at least 16 chars
       #   @see Validation::Rule::Guid
@@ -18,21 +24,15 @@ module DiasporaFederation
       #   @return [Time] Conversation creation time
       property :created_at, default: -> { Time.now.utc }
 
-      # @!attribute [r] messages
-      #   @return [[Entities::Message]] Messages of this conversation
-      entity :messages, [Entities::Message], default: []
-
-      # @!attribute [r] author
-      #   The diaspora* ID of the person initiated the conversation
-      #   @see Person#author
-      #   @return [String] diaspora* ID
-      property :author, xml_name: :diaspora_handle
-
       # @!attribute [r] participants
       #   The diaspora* IDs of the persons participating the conversation separated by ";"
       #   @return [String] participants diaspora* IDs
       property :participants, xml_name: :participant_handles
 
+      # @!attribute [r] messages
+      #   @return [[Entities::Message]] Messages of this conversation
+      entity :messages, [Entities::Message], default: []
+
       private
 
       def validate
diff --git a/lib/diaspora_federation/validators/conversation_validator.rb b/lib/diaspora_federation/validators/conversation_validator.rb
index 0001787..1aa4727 100644
--- a/lib/diaspora_federation/validators/conversation_validator.rb
+++ b/lib/diaspora_federation/validators/conversation_validator.rb
@@ -4,13 +4,13 @@ module DiasporaFederation
     class ConversationValidator < Validation::Validator
       include Validation
 
+      rule :author, %i(not_empty diaspora_id)
       rule :guid, :guid
 
-      rule :messages, :not_nil
-
-      rule :author, %i(not_empty diaspora_id)
+      rule :subject, [:not_empty, length: {maximum: 255}]
 
       rule :participants, diaspora_id_count: {maximum: 20}
+      rule :messages, :not_nil
     end
   end
 end
diff --git a/spec/lib/diaspora_federation/entities/conversation_spec.rb b/spec/lib/diaspora_federation/entities/conversation_spec.rb
index 9a794a5..bdb4746 100644
--- a/spec/lib/diaspora_federation/entities/conversation_spec.rb
+++ b/spec/lib/diaspora_federation/entities/conversation_spec.rb
@@ -22,12 +22,12 @@ module DiasporaFederation
     let(:xml) {
       <<-XML
 <conversation>
+  <diaspora_handle>#{data[:author]}</diaspora_handle>
   <guid>#{parent.guid}</guid>
   <subject>#{data[:subject]}</subject>
   <created_at>#{data[:created_at]}</created_at>
-#{data[:messages].map {|a| a.to_xml.to_s.indent(2) }.join("\n")}
-  <diaspora_handle>#{data[:author]}</diaspora_handle>
   <participant_handles>#{data[:participants]}</participant_handles>
+#{data[:messages].map {|a| a.to_xml.to_s.indent(2) }.join("\n")}
 </conversation>
 XML
     }
@@ -41,10 +41,10 @@ XML
       let(:minimal_xml) {
         <<-XML
 <conversation>
+  <author>#{data[:author]}</author>
   <guid>#{parent.guid}</guid>
   <subject>#{data[:subject]}</subject>
   <created_at>#{data[:created_at]}</created_at>
-  <author>#{data[:author]}</author>
   <participant_handles>#{data[:participants]}</participant_handles>
 </conversation>
         XML
diff --git a/spec/lib/diaspora_federation/validators/conversation_validator_spec.rb b/spec/lib/diaspora_federation/validators/conversation_validator_spec.rb
index ee2e221..2c32182 100644
--- a/spec/lib/diaspora_federation/validators/conversation_validator_spec.rb
+++ b/spec/lib/diaspora_federation/validators/conversation_validator_spec.rb
@@ -13,6 +13,14 @@ module DiasporaFederation
       let(:property) { :guid }
     end
 
+    describe "#subject" do
+      it_behaves_like "a property with a value validation/restriction" do
+        let(:property) { :subject }
+        let(:wrong_values) { [nil, "", "a" * 256] }
+        let(:correct_values) { ["a" * 255] }
+      end
+    end
+
     describe "#messages" do
       it_behaves_like "a property with a value validation/restriction" do
         let(:property) { :messages }