diff --git a/lib/block-supports/layout.php b/lib/block-supports/layout.php
index aac62e402148a..dc5fe2e6a87da 100644
--- a/lib/block-supports/layout.php
+++ b/lib/block-supports/layout.php
@@ -577,7 +577,7 @@ function gutenberg_render_layout_support_flag( $block_content, $block ) {
 
 	// Child layout specific logic.
 	if ( $child_layout ) {
-		$container_content_class   = wp_unique_id( 'wp-container-content-' );
+		$container_content_class   = wp_unique_prefixed_id( 'wp-container-content-' );
 		$child_layout_declarations = array();
 		$child_layout_styles       = array();
 
diff --git a/phpunit/block-supports/layout-test.php b/phpunit/block-supports/layout-test.php
index 6344d7617aeeb..dd40283171e5c 100644
--- a/phpunit/block-supports/layout-test.php
+++ b/phpunit/block-supports/layout-test.php
@@ -501,7 +501,7 @@ public function data_layout_support_flag_renders_classnames_on_wrapper() {
 						),
 					),
 				),
-				'expected_output' => '<p class="wp-container-content-1">Some text.</p>', // The generated classname number assumes `wp_unique_id` will not have run previously in this test.
+				'expected_output' => '<p class="wp-container-content-1">Some text.</p>', // The generated classname number assumes `wp_unique_prefixed_id( 'wp-container-content-' )` will not have run previously in this test.
 			),
 		);
 	}