diff --git a/php/WP_CLI/Runner.php b/php/WP_CLI/Runner.php
index 839ae9b99..23ed8aba8 100644
--- a/php/WP_CLI/Runner.php
+++ b/php/WP_CLI/Runner.php
@@ -1330,7 +1330,8 @@ static function ( string $arg ): string {
 				$escaped_alias = escapeshellarg( $alias );
 				$full_command  = "WP_CLI_CONFIG_PATH={$config_path} {$php_bin} {$script_path} {$escaped_alias} {$args}{$assoc_args}{$runtime_config}";
 				$pipes         = [];
-				$proc          = Utils\proc_open_compat( $full_command, [ STDIN, STDOUT, STDERR ], $pipes );
+				$env           = null;
+				$proc          = Utils\proc_open_compat( $full_command, [ STDIN, STDOUT, STDERR ], $pipes, null, $env );
 
 				if ( $proc ) {
 					$procs[] = $proc;