diff --git a/lib/compat/wordpress-5.8/index.php b/lib/compat/wordpress-5.8/index.php
index 9427ce463500af..d1dc42880061f1 100644
--- a/lib/compat/wordpress-5.8/index.php
+++ b/lib/compat/wordpress-5.8/index.php
@@ -103,3 +103,64 @@ function build_query_vars_from_query_block( $block, $page ) {
 		return $query;
 	}
 }
+
+if ( ! function_exists( 'gutenberg_register_legacy_query_loop_block' ) ) {
+	/**
+	 * Renders the legacy `core/query-loop` block on the server.
+	 * It triggers a developer warning and then calls the renamed
+	 * block's `render_callback` function output.
+	 *
+	 * @param array    $attributes Block attributes.
+	 * @param string   $content    Block default content.
+	 * @param WP_Block $block      Block instance.
+	 *
+	 * @return string Returns the output of the query, structured using the layout defined by the block's inner blocks.
+	 */
+	function gutenberg_render_legacy_query_loop_block( $attributes, $content, $block ) {
+		trigger_error(
+		/* translators: %1$s: Block type */
+			sprintf( __( 'Block %1$s has been renamed to Post Template. %1$s will be supported until WordPress version 5.9.', 'gutenberg' ), $block->name ),
+			headers_sent() || WP_DEBUG ? E_USER_WARNING : E_USER_NOTICE
+		);
+		return render_block_core_post_template( $attributes, $content, $block );
+	}
+}
+
+if ( ! function_exists( 'gutenberg_register_legacy_query_loop_block' ) ) {
+	/**
+	 * Complements the renaming of `Query Loop` to `Post Template`.
+	 * This ensures backwards compatibility for any users running the Gutenberg
+	 * plugin who have used Query Loop prior to its renaming.
+	 *
+	 * @see    https://github.com/WordPress/gutenberg/pull/32514
+	 */
+	function gutenberg_register_legacy_query_loop_block() {
+		$registry = WP_Block_Type_Registry::get_instance();
+		if ( $registry->is_registered( 'core/query-loop' ) ) {
+			unregister_block_type( 'core/query-loop' );
+		}
+		register_block_type(
+			'core/query-loop',
+			array(
+				'category'          => 'design',
+				'uses_context'      => array(
+					'queryId',
+					'query',
+					'queryContext',
+					'displayLayout',
+					'templateSlug',
+				),
+				'supports'          => array(
+					'reusable' => false,
+					'html'     => false,
+					'align'    => true,
+				),
+				'style'             => 'wp-block-post-template',
+				'render_callback'   => 'gutenberg_render_legacy_query_loop_block',
+				'skip_inner_blocks' => true,
+			)
+		);
+	}
+
+	add_action( 'init', 'gutenberg_register_legacy_query_loop_block' );
+}
diff --git a/packages/block-library/src/post-template/index.php b/packages/block-library/src/post-template/index.php
index dd69fda45fe7f3..3daacbad7f6499 100644
--- a/packages/block-library/src/post-template/index.php
+++ b/packages/block-library/src/post-template/index.php
@@ -86,63 +86,3 @@ function register_block_core_post_template() {
 	);
 }
 add_action( 'init', 'register_block_core_post_template' );
-
-/**
- * Renders the legacy `core/query-loop` block on the server.
- * It triggers a developer warning and then calls the renamed
- * block's `render_callback` function output.
- *
- * This can be removed when WordPress 5.9 is released.
- *
- * @param array    $attributes Block attributes.
- * @param string   $content    Block default content.
- * @param WP_Block $block      Block instance.
- *
- * @return string Returns the output of the query, structured using the layout defined by the block's inner blocks.
- */
-function render_legacy_query_loop_block( $attributes, $content, $block ) {
-	trigger_error(
-		/* translators: %1$s: Block type */
-		sprintf( __( 'Block %1$s has been renamed to Post Template. %1$s will be supported until WordPress version 5.9.' ), $block->name ),
-		headers_sent() || WP_DEBUG ? E_USER_WARNING : E_USER_NOTICE
-	);
-	return render_block_core_post_template( $attributes, $content, $block );
-}
-
-/**
- * Complements the renaming of `Query Loop` to `Post Template`.
- * This ensures backwards compatibility for any users running the Gutenberg
- * plugin who have used Query Loop prior to its renaming.
- *
- * This can be removed when WordPress 5.9 is released.
- *
- * @see https://github.com/WordPress/gutenberg/pull/32514
- */
-function gutenberg_register_legacy_query_loop_block() {
-	$registry = WP_Block_Type_Registry::get_instance();
-	if ( $registry->is_registered( 'core/query-loop' ) ) {
-		unregister_block_type( 'core/query-loop' );
-	}
-	register_block_type(
-		'core/query-loop',
-		array(
-			'category'          => 'design',
-			'uses_context'      => array(
-				'queryId',
-				'query',
-				'queryContext',
-				'displayLayout',
-				'templateSlug',
-			),
-			'supports'          => array(
-				'reusable' => false,
-				'html'     => false,
-				'align'    => true,
-			),
-			'style'             => 'wp-block-post-template',
-			'render_callback'   => 'render_legacy_query_loop_block',
-			'skip_inner_blocks' => true,
-		)
-	);
-}
-add_action( 'init', 'gutenberg_register_legacy_query_loop_block' );
diff --git a/packages/widgets/src/blocks/legacy-widget/index.php b/packages/widgets/src/blocks/legacy-widget/index.php
index 8a326056816c9d..e827f8f7c53096 100644
--- a/packages/widgets/src/blocks/legacy-widget/index.php
+++ b/packages/widgets/src/blocks/legacy-widget/index.php
@@ -29,6 +29,13 @@ function render_block_core_legacy_widget( $attributes ) {
 		$widget_key    = $wp_widget_factory->get_widget_key( $id_base );
 		$widget_object = $wp_widget_factory->get_widget_object( $id_base );
 	} else {
+		/*
+		 * This file is copied from the published @wordpress/widgets package when WordPress
+		 * Core is built. Because the package is a dependency of both WordPress Core and the
+		 * Gutenberg plugin where the block editor is developed, this fallback condition is
+		 * required until the minimum required version of WordPress for the plugin is raised
+		 * to 5.8.
+		 */
 		$widget_key    = gutenberg_get_widget_key( $id_base );
 		$widget_object = gutenberg_get_widget_object( $id_base );
 	}