diff --git a/specification/ilm/explain_lifecycle/types.ts b/specification/ilm/explain_lifecycle/types.ts
index 871eaf239b..d1ed0781d0 100644
--- a/specification/ilm/explain_lifecycle/types.ts
+++ b/specification/ilm/explain_lifecycle/types.ts
@@ -39,7 +39,7 @@ export class LifecycleExplainManaged {
   lifecycle_date?: DateTime
   lifecycle_date_millis?: EpochTime<UnitMillis>
   managed: true
-  phase: Name
+  phase?: Name
   phase_time?: DateTime
   phase_time_millis?: EpochTime<UnitMillis>
   policy?: Name