diff --git a/src/core/json-schema/src/formly-json-schema.service.spec.ts b/src/core/json-schema/src/formly-json-schema.service.spec.ts
index 54ee6e6c5..e1966fb82 100644
--- a/src/core/json-schema/src/formly-json-schema.service.spec.ts
+++ b/src/core/json-schema/src/formly-json-schema.service.spec.ts
@@ -162,7 +162,6 @@ describe('Service: FormlyJsonschema', () => {
             defaultValue: undefined,
             templateOptions: { ...emmptyTemplateOptions },
             fieldArray: childConfig,
-            fieldGroup: [],
          };
 
          expect(config).toEqual(baseConfig);
@@ -184,10 +183,11 @@ describe('Service: FormlyJsonschema', () => {
 
         expect(config.type).toEqual('array');
         expect(config.fieldArray).toEqual(childConfig);
+        expect(config.fieldGroup).toBeUndefined();
         // TODO: is this the best way to test this?
         // artificially increase the length of the fieldGroup
         // since the getter that is defined is based on that.
-        config.fieldGroup.push(null);
+        config.fieldGroup = [null];
         expect(config.fieldArray).toEqual(childConfig2);
         config.fieldGroup.push(null);
         expect(config.fieldArray).toEqual({});
@@ -213,7 +213,7 @@ describe('Service: FormlyJsonschema', () => {
         // TODO: is this the best way to test this?
         // artificially increase the length of the fieldGroup
         // since the getter that is defined is based on that.
-        config.fieldGroup.push(null);
+        config.fieldGroup = [null];
         expect(config.fieldArray).toEqual(childConfig2);
         config.fieldGroup.push(null);
         // should return the additional items schema when the fieldGroup's length
@@ -635,7 +635,6 @@ describe('Service: FormlyJsonschema', () => {
           type: 'array',
           defaultValue: undefined,
           templateOptions: emmptyTemplateOptions,
-          fieldGroup: [],
           fieldArray: jasmine.any(Object) as any,
         };
 
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 359252fd7..efe68db24 100644
--- a/src/core/json-schema/src/formly-json-schema.service.ts
+++ b/src/core/json-schema/src/formly-json-schema.service.ts
@@ -182,7 +182,6 @@ export class FormlyJsonschema {
 
         // TODO: remove isEnum check once adding an option to skip extension
         if (!this.isEnum(schema)) {
-          field.fieldGroup = [];
           Object.defineProperty(field, 'fieldArray', {
             get: () => {
               if (!Array.isArray(schema.items)) {
@@ -190,8 +189,9 @@ export class FormlyJsonschema {
                 return this._toFieldConfig(<JSONSchema7> schema.items, options);
               }
 
-              const itemSchema = schema.items[field.fieldGroup.length]
-                ? schema.items[field.fieldGroup.length]
+              const length = field.fieldGroup ? field.fieldGroup.length : 0;
+              const itemSchema = schema.items[length]
+                ? schema.items[length]
                 : schema.additionalItems;
 
               return itemSchema
diff --git a/src/core/src/lib/extensions/field-form/field-form.ts b/src/core/src/lib/extensions/field-form/field-form.ts
index 753cd4c90..afdfbbee3 100644
--- a/src/core/src/lib/extensions/field-form/field-form.ts
+++ b/src/core/src/lib/extensions/field-form/field-form.ts
@@ -7,11 +7,6 @@ import { registerControl } from './utils';
 /** @experimental */
 export class FieldFormExtension implements FormlyExtension {
   onPopulate(field: FormlyFieldConfigCache) {
-    // TODO: add an option to skip extension
-    if (field.fieldArray) {
-      return;
-    }
-
     if (field.key) {
       this.addFormControl(field);
     }
diff --git a/src/core/src/lib/templates/field-array.type.ts b/src/core/src/lib/templates/field-array.type.ts
index b048d4f27..2432f5a27 100644
--- a/src/core/src/lib/templates/field-array.type.ts
+++ b/src/core/src/lib/templates/field-array.type.ts
@@ -3,7 +3,7 @@ import { FormArray } from '@angular/forms';
 import { FieldType } from './field.type';
 import { clone, isNullOrUndefined, assignModelValue, getKeyPath } from '../utils';
 import { FormlyFormBuilder } from '../services/formly.form.builder';
-import { FormlyFieldConfig, FormlyFieldConfigCache } from '../components/formly.field.config';
+import { FormlyFieldConfig } from '../components/formly.field.config';
 import { FORMLY_CONFIG, FormlyExtension } from '../services/formly.config';
 import { registerControl, unregisterControl } from '../extensions/field-form/utils';
 
@@ -22,6 +22,10 @@ export abstract class FieldArrayType<F extends FormlyFieldConfig = FormlyFieldCo
   }
 
   onPopulate(field: FormlyFieldConfig) {
+    if (!field.formControl) {
+      registerControl(field, new FormArray([], { updateOn: field.modelOptions.updateOn }));
+    }
+
     field.fieldGroup = field.fieldGroup || [];
 
     const length = field.model ? field.model.length : 0;
@@ -38,17 +42,6 @@ export abstract class FieldArrayType<F extends FormlyFieldConfig = FormlyFieldCo
     }
   }
 
-  postPopulate(field: FormlyFieldConfigCache) {
-    if (field.formControl) {
-      return;
-    }
-
-    registerControl(field, new FormArray(
-      field.fieldGroup.map(f => f.formControl),
-      { updateOn: field.modelOptions.updateOn },
-    ));
-  }
-
   add(i?: number, initialModel?: any) {
     i = isNullOrUndefined(i) ? this.field.fieldGroup.length : i;
     if (!this.model) {