diff --git a/packages/ckeditor5-html-support/src/integrations/heading.ts b/packages/ckeditor5-html-support/src/integrations/heading.ts
index b80bf150240..841b096ebbf 100644
--- a/packages/ckeditor5-html-support/src/integrations/heading.ts
+++ b/packages/ckeditor5-html-support/src/integrations/heading.ts
@@ -70,5 +70,12 @@ export default class HeadingElementSupport extends Plugin {
 				allowChildren: headerModels
 			}
 		} );
+
+		dataSchema.extendBlockElement( {
+			model: 'htmlSummary',
+			modelSchema: {
+				allowChildren: headerModels
+			}
+		} );
 	}
 }
diff --git a/packages/ckeditor5-html-support/src/schemadefinitions.ts b/packages/ckeditor5-html-support/src/schemadefinitions.ts
index b84884ac726..eeb0b76d516 100644
--- a/packages/ckeditor5-html-support/src/schemadefinitions.ts
+++ b/packages/ckeditor5-html-support/src/schemadefinitions.ts
@@ -279,7 +279,15 @@ export default {
 			model: 'htmlSummary',
 			view: 'summary',
 			modelSchema: {
-				allowChildren: '$text',
+				allowChildren: [
+					'htmlH1',
+					'htmlH2',
+					'htmlH3',
+					'htmlH4',
+					'htmlH5',
+					'htmlH6',
+					'$text'
+				],
 				allowIn: 'htmlDetails',
 				isBlock: false
 			}
@@ -341,7 +349,10 @@ export default {
 			model: 'htmlHgroup',
 			view: 'hgroup',
 			modelSchema: {
+				allowIn: [ '$root', '$container' ],
 				allowChildren: [
+					'paragraph',
+					'htmlP',
 					'htmlH1',
 					'htmlH2',
 					'htmlH3',
diff --git a/packages/ckeditor5-html-support/tests/integrations/heading.js b/packages/ckeditor5-html-support/tests/integrations/heading.js
index a840e861469..e24c304db21 100644
--- a/packages/ckeditor5-html-support/tests/integrations/heading.js
+++ b/packages/ckeditor5-html-support/tests/integrations/heading.js
@@ -82,7 +82,10 @@ describe( 'HeadingElementSupport', () => {
 				model: 'htmlHgroup',
 				view: 'hgroup',
 				modelSchema: {
+					allowIn: [ '$root', '$container' ],
 					allowChildren: [
+						'paragraph',
+						'htmlP',
 						'htmlH1',
 						'htmlH2',
 						'htmlH3',
@@ -99,6 +102,30 @@ describe( 'HeadingElementSupport', () => {
 			} ] );
 		} );
 
+		it( 'should add heading models as allowed children of htmlSummary', () => {
+			expect( Array.from( dataSchema.getDefinitionsForView( 'summary' ) ) ).to.deep.equal( [ {
+				model: 'htmlSummary',
+				view: 'summary',
+				modelSchema: {
+					allowChildren: [
+						'htmlH1',
+						'htmlH2',
+						'htmlH3',
+						'htmlH4',
+						'htmlH5',
+						'htmlH6',
+						'$text',
+						'heading1',
+						'heading2',
+						'otherHeading'
+					],
+					allowIn: 'htmlDetails',
+					isBlock: false
+				},
+				isBlock: true
+			} ] );
+		} );
+
 		it( 'should preserve attributes on headings', () => {
 			const expectedHtml =
 				'<h1 data-foo="bar-1">one</h1>' +
@@ -487,7 +514,10 @@ describe( 'HeadingElementSupport', () => {
 				model: 'htmlHgroup',
 				view: 'hgroup',
 				modelSchema: {
+					allowIn: [ '$root', '$container' ],
 					allowChildren: [
+						'paragraph',
+						'htmlP',
 						'htmlH1',
 						'htmlH2',
 						'htmlH3',