Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpspec/prophecy-phpunit ^2.1.0 -> satisfiable by phpspec/prophecy-phpunit[v2.1.0, v2.2.0, v2.3.0]. - Root composer.json requires vimeo/psalm ^5.17.0 -> satisfiable by vimeo/psalm[5.17.0, ..., 5.26.1]. - vimeo/psalm[5.17.0, ..., 5.25.0] require nikic/php-parser ^4.16 -> satisfiable by nikic/php-parser[v4.16.0, ..., v4.19.4]. - vimeo/psalm[5.26.0, ..., 5.26.1] require nikic/php-parser ^4.17 -> satisfiable by nikic/php-parser[v4.17.0, ..., v4.19.4]. - Conclusion: install nikic/php-parser v5.4.0 (conflict analysis result) - You can only install one version of a package, so only one of these can be installed: nikic/php-parser[v4.16.0, ..., v4.19.4, v5.0.0, ..., v5.4.0]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.