diff --git a/src/wp-includes/rest-api.php b/src/wp-includes/rest-api.php
index 2c0e8f7e18..5cd7ef8774 100644
--- a/src/wp-includes/rest-api.php
+++ b/src/wp-includes/rest-api.php
@@ -1311,3 +1311,56 @@ function rest_sanitize_value_from_schema( $value, $args ) {
 
 	return $value;
 }
+
+/**
+ * Append result of internal request to REST API for purpose of preloading data to be attached to a page.
+ * Expected to be called in the context of `array_reduce`.
+ *
+ * @since 5.0.0
+ *
+ * @param  array  $memo Reduce accumulator.
+ * @param  string $path REST API path to preload.
+ * @return array        Modified reduce accumulator.
+ */
+function rest_preload_api_request( $memo, $path ) {
+	// array_reduce() doesn't support passing an array in PHP 5.2, so we need to make sure we start with one.
+	if ( ! is_array( $memo ) ) {
+		$memo = array();
+	}
+
+	if ( empty( $path ) ) {
+		return $memo;
+	}
+
+	$path_parts = parse_url( $path );
+	if ( false === $path_parts ) {
+		return $memo;
+	}
+
+	$request = new WP_REST_Request( 'GET', $path_parts['path'] );
+	if ( ! empty( $path_parts['query'] ) ) {
+		parse_str( $path_parts['query'], $query_params );
+		$request->set_query_params( $query_params );
+	}
+
+	$response = rest_do_request( $request );
+	if ( 200 === $response->status ) {
+		$server = rest_get_server();
+		$data   = (array) $response->get_data();
+		if ( method_exists( $server, 'get_compact_response_links' ) ) {
+			$links = call_user_func( array( $server, 'get_compact_response_links' ), $response );
+		} else {
+			$links = call_user_func( array( $server, 'get_response_links' ), $response );
+		}
+		if ( ! empty( $links ) ) {
+			$data['_links'] = $links;
+		}
+
+		$memo[ $path ] = array(
+			'body'    => $data,
+			'headers' => $response->headers,
+		);
+	}
+
+	return $memo;
+}
diff --git a/tests/phpunit/tests/rest-api.php b/tests/phpunit/tests/rest-api.php
index 52c30dc471..d20566e15e 100644
--- a/tests/phpunit/tests/rest-api.php
+++ b/tests/phpunit/tests/rest-api.php
@@ -712,4 +712,13 @@ class Tests_REST_API extends WP_UnitTestCase {
 		$routes = $GLOBALS['wp_rest_server']->get_routes();
 		$this->assertEquals( $routes['/test-ns/test'][0]['methods'], array( 'GET' => true ) );
 	}
+
+	/**
+	 * Ensure rest_preload_api_request() works without notices in PHP 5.2.
+	 *
+	 * The array_reduce() function only accepts mixed variables starting with PHP 5.3.
+	 */
+	function test_rest_preload_api_request_no_notices_php_52() {
+		$this->assertTrue( is_array( rest_preload_api_request( 0, '/' ) ) );
+	}
 }