diff --git a/packages/block-library/src/heading/editor.scss b/packages/block-library/src/heading/editor.scss
index 05040868113b6..0add23862762f 100644
--- a/packages/block-library/src/heading/editor.scss
+++ b/packages/block-library/src/heading/editor.scss
@@ -13,6 +13,6 @@
 	border: none;
 }
 
-.block-library-heading__heading-level-checker {
+.block-library-heading__heading-level-checker-warning {
 	margin: 0;
 }
diff --git a/packages/block-library/src/heading/heading-level-checker.js b/packages/block-library/src/heading/heading-level-checker.js
index a206c3251abc9..75ae039eca129 100644
--- a/packages/block-library/src/heading/heading-level-checker.js
+++ b/packages/block-library/src/heading/heading-level-checker.js
@@ -1,19 +1,22 @@
 /**
  * External dependencies
  */
-import { countBy, flatMap, get } from 'lodash';
+import { flatMap } from 'lodash';
 
 /**
  * WordPress dependencies
  */
 import { speak } from '@wordpress/a11y';
-import { __ } from '@wordpress/i18n';
 import { Notice } from '@wordpress/components';
+import { useSelect } from '@wordpress/data';
 import { useEffect } from '@wordpress/element';
-import { compose } from '@wordpress/compose';
-import { withSelect } from '@wordpress/data';
+import { __ } from '@wordpress/i18n';
+
+const INVALID_LEVEL_MESSAGE = __(
+	'The selected heading level may be invalid. See the content structure tool for more info.'
+);
 
-// copy from packages/editor/src/components/document-outline/index.js
+// Copied from packages/editor/src/components/document-outline/index.js.
 /**
  * Returns an array of heading blocks enhanced with the following properties:
  * path    - An array of blocks that are ancestors of the heading starting from a top-level node.
@@ -26,7 +29,8 @@ import { withSelect } from '@wordpress/data';
  *
  * @return {Array} An array of heading blocks enhanced with the properties described above.
  */
-export const computeOutlineHeadings = ( blocks = [], path = [] ) => {
+function computeOutlineHeadings( blocks = [], path = [] ) {
+	// We don't polyfill native JS [].flatMap yet, so we have to use Lodash.
 	return flatMap( blocks, ( block = {} ) => {
 		if ( block.name === 'core/heading' ) {
 			return {
@@ -37,71 +41,70 @@ export const computeOutlineHeadings = ( blocks = [], path = [] ) => {
 		}
 		return computeOutlineHeadings( block.innerBlocks, [ ...path, block ] );
 	} );
-};
+}
 
-export const HeadingLevelChecker = ( {
-	blocks = [],
-	title,
-	isTitleSupported,
-	selectedHeadingId,
-} ) => {
-	const headings = computeOutlineHeadings( blocks );
+export default function HeadingLevelChecker( { selectedHeadingId } ) {
+	const { headings, titleIsNotEmpty, isTitleSupported } = useSelect(
+		( select ) => {
+			const { getPostType } = select( 'core' );
+			const { getBlocks } = select( 'core/block-editor' );
+			const { getEditedPostAttribute } = select( 'core/editor' );
+			const postType = getPostType( getEditedPostAttribute( 'type' ) );
 
-	// Iterate headings to find prevHeadingLevel and selectedLevel
-	let prevHeadingLevel = 1;
+			return {
+				headings: computeOutlineHeadings( getBlocks() ?? [] ),
+				titleIsNotEmpty: !! getEditedPostAttribute( 'title' ),
+				isTitleSupported: postType?.supports?.title ?? false,
+			};
+		},
+		[]
+	);
+
+	// Find the heading level of the current block and the level of the closest
+	// heading preceding it.
+	let prevLevel = 1;
 	let selectedLevel = 1;
-	let i = 0;
-	for ( i = 0; i < headings.length; i++ ) {
+	for ( let i = 0; i < headings.length; i++ ) {
 		if ( headings[ i ].clientId === selectedHeadingId ) {
 			selectedLevel = headings[ i ].level;
 			if ( i >= 1 ) {
-				prevHeadingLevel = headings[ i - 1 ].level;
+				prevLevel = headings[ i - 1 ].level;
 			}
 		}
 	}
 
-	const titleNode = document.querySelector( '.editor-post-title__input' );
-	const hasTitle = isTitleSupported && title && titleNode;
-	const countByLevel = countBy( headings, 'level' );
-	const hasMultipleH1 = countByLevel[ 1 ] > 1;
-	const isIncorrectLevel = selectedLevel > prevHeadingLevel + 1;
+	const titleNode = document.getElementsByClassName(
+		'editor-post-title__input'
+	)[ 0 ];
+	const hasTitle = isTitleSupported && titleIsNotEmpty && titleNode;
+	const hasMultipleH1 =
+		headings.filter( ( { level } ) => level === 1 ).length > 1;
+	const levelIsDuplicateH1 = hasMultipleH1 && selectedLevel === 1;
+	const levelAndPostTitleAreBothH1 =
+		selectedLevel === 1 && hasTitle && ! hasMultipleH1;
+	const levelIsTooDeep = selectedLevel > prevLevel + 1;
+	const levelIsInvalid =
+		levelIsDuplicateH1 || levelAndPostTitleAreBothH1 || levelIsTooDeep;
 
-	// For accessibility
+	// For accessibility, announce the invalid heading level to screen readers.
+	// The selectedLevel value is included in the dependency array so that the
+	// message will be replayed if a new level is selected, but the new level is
+	// still invalid.
 	useEffect( () => {
-		if ( isIncorrectLevel ) speak( msg );
-	}, [ isIncorrectLevel, selectedLevel ] );
+		if ( levelIsInvalid ) speak( INVALID_LEVEL_MESSAGE );
+	}, [ selectedLevel, levelIsInvalid ] );
 
-	let msg = '';
-	if ( isIncorrectLevel ) {
-		msg = __( 'This heading level is incorrect.' );
-	} else if ( selectedLevel === 1 && hasMultipleH1 ) {
-		msg = __( 'Multiple H1 headings found.' );
-	} else if ( selectedLevel === 1 && hasTitle && ! hasMultipleH1 ) {
-		msg = __( 'H1 is already used for the post title.' );
-	} else {
+	if ( ! levelIsInvalid ) {
 		return null;
 	}
 
 	return (
-		<div className="block-library-heading__heading-level-checker">
-			<Notice status="warning" isDismissible={ false }>
-				{ msg }
-			</Notice>
-		</div>
+		<Notice
+			className="block-library-heading__heading-level-checker-warning"
+			isDismissible={ false }
+			status="warning"
+		>
+			{ INVALID_LEVEL_MESSAGE }
+		</Notice>
 	);
-};
-
-export default compose(
-	withSelect( ( select ) => {
-		const { getBlocks } = select( 'core/block-editor' );
-		const { getEditedPostAttribute } = select( 'core/editor' );
-		const { getPostType } = select( 'core' );
-		const postType = getPostType( getEditedPostAttribute( 'type' ) );
-
-		return {
-			blocks: getBlocks(),
-			title: getEditedPostAttribute( 'title' ),
-			isTitleSupported: get( postType, [ 'supports', 'title' ], false ),
-		};
-	} )
-)( HeadingLevelChecker );
+}