diff --git a/src/core/json-schema/src/formly-json-schema.service.ts b/src/core/json-schema/src/formly-json-schema.service.ts
index 45c458f8d..db31f5ecc 100644
--- a/src/core/json-schema/src/formly-json-schema.service.ts
+++ b/src/core/json-schema/src/formly-json-schema.service.ts
@@ -7,6 +7,7 @@ import {
   ɵgetFieldInitialValue as getFieldInitialValue,
   ɵclone as clone,
 } from '@ngx-formly/core';
+import { tap } from 'rxjs/operators';
 
 export interface FormlyJsonschemaOptions {
   /**
@@ -365,6 +366,11 @@ export class FormlyJsonschema {
             options: schemas
               .map((s, i) => ({ label: s.title, value: i, disabled: s.readOnly })),
           },
+          hooks: {
+            onInit: f => f.formControl.valueChanges.pipe(
+              tap(() => (f.options as any)._checkField(f.parent)),
+            ),
+          },
         },
         {
           fieldGroup: schemas.map((s, i) => ({