diff --git a/lib/diaspora_federation/entities/comment.rb b/lib/diaspora_federation/entities/comment.rb
index e5157a6..b54c5e7 100644
--- a/lib/diaspora_federation/entities/comment.rb
+++ b/lib/diaspora_federation/entities/comment.rb
@@ -23,8 +23,8 @@ module DiasporaFederation
       property :diaspora_id, xml_name: :diaspora_handle
 
       # The {Comment} parent is a Post
-      # @return [String] target type
-      def target_type
+      # @return [String] parent type
+      def parent_type
         "Post"
       end
     end
diff --git a/lib/diaspora_federation/entities/like.rb b/lib/diaspora_federation/entities/like.rb
index 89b92b0..a0d836d 100644
--- a/lib/diaspora_federation/entities/like.rb
+++ b/lib/diaspora_federation/entities/like.rb
@@ -16,12 +16,12 @@ module DiasporaFederation
       #   @return [String] like guid
       property :guid
 
-      # @!attribute [r] target_type
-      #   A string describing the type of the target.
+      # @!attribute [r] parent_type
+      #   A string describing the type of the parent.
       #   Can be "Post" or "Comment" (Comments are currently not implemented in the
       #   Diaspora Frontend).
-      #   @return [String] target type
-      property :target_type
+      #   @return [String] parent type
+      property :parent_type, xml_name: :target_type
 
       include Relayable
 
diff --git a/lib/diaspora_federation/entities/message.rb b/lib/diaspora_federation/entities/message.rb
index 3d8116e..1a9096f 100644
--- a/lib/diaspora_federation/entities/message.rb
+++ b/lib/diaspora_federation/entities/message.rb
@@ -35,8 +35,8 @@ module DiasporaFederation
       property :conversation_guid
 
       # The {Message} parent is a {Conversation}
-      # @return [String] target type
-      def target_type
+      # @return [String] parent type
+      def parent_type
         "Conversation"
       end
     end
diff --git a/lib/diaspora_federation/entities/participation.rb b/lib/diaspora_federation/entities/participation.rb
index 8c628d7..e57dc20 100644
--- a/lib/diaspora_federation/entities/participation.rb
+++ b/lib/diaspora_federation/entities/participation.rb
@@ -10,11 +10,11 @@ module DiasporaFederation
       #   @return [String] participation guid
       property :guid
 
-      # @!attribute [r] target_type
+      # @!attribute [r] parent_type
       #   a string describing a type of the target to subscribe on.
       #   currently only "Post" is supported.
-      #   @return [String] target type
-      property :target_type
+      #   @return [String] parent type
+      property :parent_type, xml_name: :target_type
 
       include Relayable
 
diff --git a/lib/diaspora_federation/entities/poll_participation.rb b/lib/diaspora_federation/entities/poll_participation.rb
index a994505..964012a 100644
--- a/lib/diaspora_federation/entities/poll_participation.rb
+++ b/lib/diaspora_federation/entities/poll_participation.rb
@@ -25,8 +25,8 @@ module DiasporaFederation
       property :poll_answer_guid
 
       # The {PollParticipation} parent is a {Poll}
-      # @return [String] target type
-      def target_type
+      # @return [String] parent type
+      def parent_type
         "Poll"
       end
     end
diff --git a/lib/diaspora_federation/entities/relayable.rb b/lib/diaspora_federation/entities/relayable.rb
index 39215c5..ce4b9b2 100644
--- a/lib/diaspora_federation/entities/relayable.rb
+++ b/lib/diaspora_federation/entities/relayable.rb
@@ -48,7 +48,7 @@ module DiasporaFederation
 
           if parent_author_signature.nil?
             privkey = DiasporaFederation.callbacks.trigger(
-              :fetch_author_private_key_by_entity_guid, target_type, parent_guid
+              :fetch_author_private_key_by_entity_guid, parent_type, parent_guid
             )
             hash[:parent_author_signature] = Signing.sign_with_key(hash, privkey) unless privkey.nil?
           end
@@ -79,7 +79,7 @@ module DiasporaFederation
           data, author_signature, pubkey
         )
 
-        author_is_local = DiasporaFederation.callbacks.trigger(:entity_author_is_local?, target_type, parent_guid)
+        author_is_local = DiasporaFederation.callbacks.trigger(:entity_author_is_local?, parent_type, parent_guid)
         verify_parent_signature unless author_is_local
       end
 
@@ -87,7 +87,7 @@ module DiasporaFederation
 
       # this happens only on downstream federation
       def verify_parent_signature
-        pubkey = DiasporaFederation.callbacks.trigger(:fetch_author_public_key_by_entity_guid, target_type, parent_guid)
+        pubkey = DiasporaFederation.callbacks.trigger(:fetch_author_public_key_by_entity_guid, parent_type, parent_guid)
 
         raise SignatureVerificationFailed, "failed to fetch public key for author of #{parent_guid}" if pubkey.nil?
         raise SignatureVerificationFailed, "wrong parent_author_signature" unless Signing.verify_signature(
diff --git a/lib/diaspora_federation/test/factories.rb b/lib/diaspora_federation/test/factories.rb
index 7d2d691..3248b46 100644
--- a/lib/diaspora_federation/test/factories.rb
+++ b/lib/diaspora_federation/test/factories.rb
@@ -92,7 +92,7 @@ module DiasporaFederation
           factory :participation_entity,
                   class: DiasporaFederation::Entities::Participation, parent: :relayable_entity do
             guid
-            target_type "Post"
+            parent_type "Post"
             diaspora_id
           end
 
@@ -118,7 +118,7 @@ module DiasporaFederation
           factory :like_entity, class: DiasporaFederation::Entities::Like, parent: :relayable_entity do
             positive true
             guid
-            target_type "Post"
+            parent_type "Post"
             diaspora_id
           end
 
diff --git a/lib/diaspora_federation/validators/like_validator.rb b/lib/diaspora_federation/validators/like_validator.rb
index f7222f8..2f5df43 100644
--- a/lib/diaspora_federation/validators/like_validator.rb
+++ b/lib/diaspora_federation/validators/like_validator.rb
@@ -6,6 +6,8 @@ module DiasporaFederation
 
       rule :guid, :guid
 
+      rule :parent_type, [:not_empty, regular_expression: {regex: /\A(Post|Comment)\z/}]
+
       include RelayableValidator
 
       rule :diaspora_id, %i(not_empty diaspora_id)
diff --git a/lib/diaspora_federation/validators/participation_validator.rb b/lib/diaspora_federation/validators/participation_validator.rb
index 5f3921e..4ce797a 100644
--- a/lib/diaspora_federation/validators/participation_validator.rb
+++ b/lib/diaspora_federation/validators/participation_validator.rb
@@ -6,7 +6,7 @@ module DiasporaFederation
 
       rule :guid, :guid
 
-      rule :target_type, :not_empty
+      rule :parent_type, [:not_empty, regular_expression: {regex: /\APost\z/}]
 
       include RelayableValidator
 
diff --git a/spec/lib/diaspora_federation/entities/comment_spec.rb b/spec/lib/diaspora_federation/entities/comment_spec.rb
index ff39430..75b8656 100644
--- a/spec/lib/diaspora_federation/entities/comment_spec.rb
+++ b/spec/lib/diaspora_federation/entities/comment_spec.rb
@@ -21,9 +21,9 @@ XML
 
     it_behaves_like "a relayable Entity"
 
-    describe "#target_type" do
-      it "returns \"Post\" as target type" do
-        expect(described_class.new(data).target_type).to eq("Post")
+    describe "#parent_type" do
+      it "returns \"Post\" as parent type" do
+        expect(described_class.new(data).parent_type).to eq("Post")
       end
     end
   end
diff --git a/spec/lib/diaspora_federation/entities/like_spec.rb b/spec/lib/diaspora_federation/entities/like_spec.rb
index 5821f7e..7782f4a 100644
--- a/spec/lib/diaspora_federation/entities/like_spec.rb
+++ b/spec/lib/diaspora_federation/entities/like_spec.rb
@@ -7,7 +7,7 @@ module DiasporaFederation
 <like>
   <positive>#{data[:positive]}</positive>
   <guid>#{data[:guid]}</guid>
-  <target_type>#{data[:target_type]}</target_type>
+  <target_type>#{data[:parent_type]}</target_type>
   <parent_guid>#{data[:parent_guid]}</parent_guid>
   <parent_author_signature>#{data[:parent_author_signature]}</parent_author_signature>
   <author_signature>#{data[:author_signature]}</author_signature>
@@ -22,9 +22,9 @@ XML
 
     it_behaves_like "a relayable Entity"
 
-    describe "#target_type" do
-      it "returns data[:target_type] as target type" do
-        expect(described_class.new(data).target_type).to eq(data[:target_type])
+    describe "#parent_type" do
+      it "returns data[:parent_type] as parent type" do
+        expect(described_class.new(data).parent_type).to eq(data[:parent_type])
       end
     end
   end
diff --git a/spec/lib/diaspora_federation/entities/message_spec.rb b/spec/lib/diaspora_federation/entities/message_spec.rb
index e181920..c023fc7 100644
--- a/spec/lib/diaspora_federation/entities/message_spec.rb
+++ b/spec/lib/diaspora_federation/entities/message_spec.rb
@@ -23,9 +23,9 @@ XML
 
     it_behaves_like "a relayable Entity"
 
-    describe "#target_type" do
-      it "returns \"Conversation\" as target type" do
-        expect(described_class.new(data).target_type).to eq("Conversation")
+    describe "#parent_type" do
+      it "returns \"Conversation\" as parent type" do
+        expect(described_class.new(data).parent_type).to eq("Conversation")
       end
     end
   end
diff --git a/spec/lib/diaspora_federation/entities/participation_spec.rb b/spec/lib/diaspora_federation/entities/participation_spec.rb
index cf41587..7007880 100644
--- a/spec/lib/diaspora_federation/entities/participation_spec.rb
+++ b/spec/lib/diaspora_federation/entities/participation_spec.rb
@@ -6,7 +6,7 @@ module DiasporaFederation
       <<-XML
 <participation>
   <guid>#{data[:guid]}</guid>
-  <target_type>#{data[:target_type]}</target_type>
+  <target_type>#{data[:parent_type]}</target_type>
   <parent_guid>#{data[:parent_guid]}</parent_guid>
   <parent_author_signature>#{data[:parent_author_signature]}</parent_author_signature>
   <author_signature>#{data[:author_signature]}</author_signature>
@@ -21,9 +21,9 @@ XML
 
     it_behaves_like "a relayable Entity"
 
-    describe "#target_type" do
-      it "returns data[:target_type] as target type" do
-        expect(described_class.new(data).target_type).to eq(data[:target_type])
+    describe "#parent_type" do
+      it "returns data[:parent_type] as parent type" do
+        expect(described_class.new(data).parent_type).to eq(data[:parent_type])
       end
     end
   end
diff --git a/spec/lib/diaspora_federation/entities/poll_participation_spec.rb b/spec/lib/diaspora_federation/entities/poll_participation_spec.rb
index 73ccc7f..f60fa96 100644
--- a/spec/lib/diaspora_federation/entities/poll_participation_spec.rb
+++ b/spec/lib/diaspora_federation/entities/poll_participation_spec.rb
@@ -21,9 +21,9 @@ XML
 
     it_behaves_like "a relayable Entity"
 
-    describe "#target_type" do
-      it "returns \"Poll\" as target type" do
-        expect(described_class.new(data).target_type).to eq("Poll")
+    describe "#parent_type" do
+      it "returns \"Poll\" as parent type" do
+        expect(described_class.new(data).parent_type).to eq("Poll")
       end
     end
   end
diff --git a/spec/lib/diaspora_federation/entities/relayable_spec.rb b/spec/lib/diaspora_federation/entities/relayable_spec.rb
index 16cfbbd..3a75702 100644
--- a/spec/lib/diaspora_federation/entities/relayable_spec.rb
+++ b/spec/lib/diaspora_federation/entities/relayable_spec.rb
@@ -15,7 +15,7 @@ module DiasporaFederation
 
       property :diaspora_id, xml_name: :diaspora_handle
 
-      def target_type
+      def parent_type
         "Target"
       end
     end
diff --git a/spec/lib/diaspora_federation/validators/like_validator_spec.rb b/spec/lib/diaspora_federation/validators/like_validator_spec.rb
index c6fcb11..6376c21 100644
--- a/spec/lib/diaspora_federation/validators/like_validator_spec.rb
+++ b/spec/lib/diaspora_federation/validators/like_validator_spec.rb
@@ -15,5 +15,13 @@ module DiasporaFederation
       let(:property) { :diaspora_id }
       let(:mandatory) { true }
     end
+
+    describe "#parent_type" do
+      it_behaves_like "a property with a value validation/restriction" do
+        let(:property) { :parent_type }
+        let(:wrong_values) { [nil, "", "any", "Postxxx", "post"] }
+        let(:correct_values) { %w(Post Comment) }
+      end
+    end
   end
 end
diff --git a/spec/lib/diaspora_federation/validators/participation_validator_spec.rb b/spec/lib/diaspora_federation/validators/participation_validator_spec.rb
index 0a1f451..fad742a 100644
--- a/spec/lib/diaspora_federation/validators/participation_validator_spec.rb
+++ b/spec/lib/diaspora_federation/validators/participation_validator_spec.rb
@@ -17,9 +17,11 @@ module DiasporaFederation
       end
     end
 
-    describe "#target_type" do
-      it_behaves_like "a property that mustn't be empty" do
-        let(:property) { :target_type }
+    describe "#parent_type" do
+      it_behaves_like "a property with a value validation/restriction" do
+        let(:property) { :parent_type }
+        let(:wrong_values) { [nil, "", "any", "Postxxx", "post"] }
+        let(:correct_values) { ["Post"] }
       end
     end
   end
diff --git a/spec/lib/diaspora_federation/validators/retraction_validator_spec.rb b/spec/lib/diaspora_federation/validators/retraction_validator_spec.rb
index 53a0729..a337ab6 100644
--- a/spec/lib/diaspora_federation/validators/retraction_validator_spec.rb
+++ b/spec/lib/diaspora_federation/validators/retraction_validator_spec.rb
@@ -12,7 +12,7 @@ module DiasporaFederation
       let(:mandatory) { true }
     end
 
-    describe "#type" do
+    describe "#target_type" do
       it_behaves_like "a property that mustn't be empty" do
         let(:property) { :target_type }
       end