diff --git a/x-pack/plugins/ml/server/routes/schemas/anomaly_detectors_schema.ts b/x-pack/plugins/ml/server/routes/schemas/anomaly_detectors_schema.ts
index 196e17d0984f..9203c7cf997a 100644
--- a/x-pack/plugins/ml/server/routes/schemas/anomaly_detectors_schema.ts
+++ b/x-pack/plugins/ml/server/routes/schemas/anomaly_detectors_schema.ts
@@ -11,7 +11,7 @@ const customRulesSchema = schema.maybe(
     schema.maybe(
       schema.object({
         actions: schema.arrayOf(schema.string()),
-        conditions: schema.arrayOf(schema.any()),
+        conditions: schema.maybe(schema.arrayOf(schema.any())),
         scope: schema.maybe(schema.any()),
       })
     )