Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires nettrine/fixtures ^0.8.0 -> satisfiable by nettrine/fixtures[v0.8.0]. - Root composer.json requires nettrine/orm ^0.9.0 -> satisfiable by nettrine/orm[v0.9.0]. - doctrine/orm[3.3.0, ..., 3.4.x-dev] require doctrine/lexer ^3 -> satisfiable by doctrine/lexer[3.0.0, 3.0.1, 3.0.x-dev, 3.1.x-dev]. - nettrine/fixtures v0.8.0 requires doctrine/orm ^3.3.0 -> satisfiable by doctrine/orm[3.3.0, 3.3.1, 3.3.x-dev, 3.4.x-dev]. - Conclusion: don't install doctrine/lexer 3.0.1 (conflict analysis result) Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.