diff --git a/app/services/concerns/payloadable.rb b/app/services/concerns/payloadable.rb
index bd9d9d74b5..73c397852e 100644
--- a/app/services/concerns/payloadable.rb
+++ b/app/services/concerns/payloadable.rb
@@ -17,7 +17,7 @@ module Payloadable
     payload     = ActiveModelSerializers::SerializableResource.new(record, options.merge(serializer: serializer, adapter: ActivityPub::Adapter)).as_json
     object      = record.respond_to?(:virtual_object) ? record.virtual_object : record
 
-    if (object.respond_to?(:sign?) && object.sign?) && signer && (always_sign || signing_enabled?)
+    if ((object.respond_to?(:sign?) && object.sign?) && signer && (always_sign || signing_enabled?)) || object.is_a?(String)
       ActivityPub::LinkedDataSignature.new(payload).sign!(signer, sign_with: sign_with)
     else
       payload