diff --git a/lib/tasks/task.js b/lib/tasks/task.js
index 7c683c4e..ba6cd530 100644
--- a/lib/tasks/task.js
+++ b/lib/tasks/task.js
@@ -336,6 +336,9 @@ class Task extends Emitter {
         }
         required = required.filter((item) => item !== dKey);
       }
+      else if (dKey === '_') {
+        /* no op: allow arbitrary info to be carried here, used by conference e.g in transfer */
+      }
       else throw new Error(`${name}: unknown property ${dKey}`);
     }
     if (required.length > 0) throw new Error(`${name}: missing value for ${required}`);