diff --git a/pep508.nix b/pep508.nix
index 9c95194..5098c5c 100644
--- a/pep508.nix
+++ b/pep508.nix
@@ -160,12 +160,12 @@ let
       hasElem = needle: haystack: builtins.elem needle (builtins.filter (x: builtins.typeOf x == "string") (builtins.split " " haystack));
       op = {
         "true" = x: y: true;
-        "<=" = x: y: (unmarshal x) <= (unmarshal y);
-        "<" = x: y: (unmarshal x) < (unmarshal y);
+        "<=" = x: y: op.">=" y x;
+        "<" = x: y: lib.versionOlder (unmarshal x) (unmarshal y);
         "!=" = x: y: x != y;
         "==" = x: y: x == y;
-        ">=" = x: y: (unmarshal x) >= (unmarshal y);
-        ">" = x: y: (unmarshal x) > (unmarshal y);
+        ">=" = x: y: lib.versionAtLeast (unmarshal x) (unmarshal y);
+        ">" = x: y: op."<" y x;
         "~=" = v: c:
           let
             parts = builtins.splitVersion c;
diff --git a/tests/default.nix b/tests/default.nix
index dc2763c..2cc8440 100644
--- a/tests/default.nix
+++ b/tests/default.nix
@@ -28,6 +28,7 @@ builtins.removeAttrs
   top-packages-2 = callTest ./common-pkgs-2 { };
   pep425 = pkgs.callPackage ./pep425 { inherit pep425;inherit pep425OSX;inherit pep425Python37; };
   env = callTest ./env { };
+  pytest-randomly = callTest ./pytest-randomly { };
   file-src-deps = callTest ./file-src-deps { };
   file-src-deps-level2 = callTest ./file-src-deps-level2 { };
   file-wheel-deps = callTest ./file-wheel-deps { };
diff --git a/tests/pytest-randomly/default.nix b/tests/pytest-randomly/default.nix
new file mode 100644
index 0000000..ed15669
--- /dev/null
+++ b/tests/pytest-randomly/default.nix
@@ -0,0 +1,13 @@
+{ lib, poetry2nix, python39, runCommand }:
+let
+  env = poetry2nix.mkPoetryEnv {
+    python = python39;
+    pyproject = ./pyproject.toml;
+    poetrylock = ./poetry.lock;
+  };
+in
+runCommand "pytest_randomly"
+{ } ''
+  ${env}/bin/python -c 'import pytest_randomly'
+  touch $out
+''
diff --git a/tests/pytest-randomly/poetry.lock b/tests/pytest-randomly/poetry.lock
new file mode 100644
index 0000000..721ea8f
--- /dev/null
+++ b/tests/pytest-randomly/poetry.lock
@@ -0,0 +1,204 @@
+[[package]]
+name = "atomicwrites"
+version = "1.4.0"
+description = "Atomic file writes."
+category = "main"
+optional = false
+python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
+
+[[package]]
+name = "attrs"
+version = "21.2.0"
+description = "Classes Without Boilerplate"
+category = "main"
+optional = false
+python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
+
+[package.extras]
+dev = ["coverage[toml] (>=5.0.2)", "hypothesis", "pympler", "pytest (>=4.3.0)", "six", "mypy", "pytest-mypy-plugins", "zope.interface", "furo", "sphinx", "sphinx-notfound-page", "pre-commit"]
+docs = ["furo", "sphinx", "zope.interface", "sphinx-notfound-page"]
+tests = ["coverage[toml] (>=5.0.2)", "hypothesis", "pympler", "pytest (>=4.3.0)", "six", "mypy", "pytest-mypy-plugins", "zope.interface"]
+tests_no_zope = ["coverage[toml] (>=5.0.2)", "hypothesis", "pympler", "pytest (>=4.3.0)", "six", "mypy", "pytest-mypy-plugins"]
+
+[[package]]
+name = "colorama"
+version = "0.4.4"
+description = "Cross-platform colored terminal text."
+category = "main"
+optional = false
+python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
+
+[[package]]
+name = "importlib-metadata"
+version = "4.8.1"
+description = "Read metadata from Python packages"
+category = "main"
+optional = false
+python-versions = ">=3.6"
+
+[package.dependencies]
+zipp = ">=0.5"
+
+[package.extras]
+docs = ["sphinx", "jaraco.packaging (>=8.2)", "rst.linker (>=1.9)"]
+perf = ["ipython"]
+testing = ["pytest (>=4.6)", "pytest-checkdocs (>=2.4)", "pytest-flake8", "pytest-cov", "pytest-enabler (>=1.0.1)", "packaging", "pep517", "pyfakefs", "flufl.flake8", "pytest-perf (>=0.9.2)", "pytest-black (>=0.3.7)", "pytest-mypy", "importlib-resources (>=1.3)"]
+
+[[package]]
+name = "iniconfig"
+version = "1.1.1"
+description = "iniconfig: brain-dead simple config-ini parsing"
+category = "main"
+optional = false
+python-versions = "*"
+
+[[package]]
+name = "packaging"
+version = "21.0"
+description = "Core utilities for Python packages"
+category = "main"
+optional = false
+python-versions = ">=3.6"
+
+[package.dependencies]
+pyparsing = ">=2.0.2"
+
+[[package]]
+name = "pluggy"
+version = "1.0.0"
+description = "plugin and hook calling mechanisms for python"
+category = "main"
+optional = false
+python-versions = ">=3.6"
+
+[package.extras]
+dev = ["pre-commit", "tox"]
+testing = ["pytest", "pytest-benchmark"]
+
+[[package]]
+name = "py"
+version = "1.10.0"
+description = "library with cross-python path, ini-parsing, io, code, log facilities"
+category = "main"
+optional = false
+python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
+
+[[package]]
+name = "pyparsing"
+version = "2.4.7"
+description = "Python parsing module"
+category = "main"
+optional = false
+python-versions = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*"
+
+[[package]]
+name = "pytest"
+version = "6.2.5"
+description = "pytest: simple powerful testing with Python"
+category = "main"
+optional = false
+python-versions = ">=3.6"
+
+[package.dependencies]
+atomicwrites = {version = ">=1.0", markers = "sys_platform == \"win32\""}
+attrs = ">=19.2.0"
+colorama = {version = "*", markers = "sys_platform == \"win32\""}
+iniconfig = "*"
+packaging = "*"
+pluggy = ">=0.12,<2.0"
+py = ">=1.8.2"
+toml = "*"
+
+[package.extras]
+testing = ["argcomplete", "hypothesis (>=3.56)", "mock", "nose", "requests", "xmlschema"]
+
+[[package]]
+name = "pytest-randomly"
+version = "3.10.1"
+description = "Pytest plugin to randomly order tests and control random.seed."
+category = "main"
+optional = false
+python-versions = ">=3.6"
+
+[package.dependencies]
+importlib-metadata = {version = ">=3.6.0", markers = "python_version < \"3.10\""}
+pytest = "*"
+
+[[package]]
+name = "toml"
+version = "0.10.2"
+description = "Python Library for Tom's Obvious, Minimal Language"
+category = "main"
+optional = false
+python-versions = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*"
+
+[[package]]
+name = "zipp"
+version = "3.5.0"
+description = "Backport of pathlib-compatible object wrapper for zip files"
+category = "main"
+optional = false
+python-versions = ">=3.6"
+
+[package.extras]
+docs = ["sphinx", "jaraco.packaging (>=8.2)", "rst.linker (>=1.9)"]
+testing = ["pytest (>=4.6)", "pytest-checkdocs (>=2.4)", "pytest-flake8", "pytest-cov", "pytest-enabler (>=1.0.1)", "jaraco.itertools", "func-timeout", "pytest-black (>=0.3.7)", "pytest-mypy"]
+
+[metadata]
+lock-version = "1.1"
+python-versions = "^3.8"
+content-hash = "bd925bd34dd039030faf8b7416bfee5a53957b2819216e2a80f7a70d04e28b2e"
+
+[metadata.files]
+atomicwrites = [
+    {file = "atomicwrites-1.4.0-py2.py3-none-any.whl", hash = "sha256:6d1784dea7c0c8d4a5172b6c620f40b6e4cbfdf96d783691f2e1302a7b88e197"},
+    {file = "atomicwrites-1.4.0.tar.gz", hash = "sha256:ae70396ad1a434f9c7046fd2dd196fc04b12f9e91ffb859164193be8b6168a7a"},
+]
+attrs = [
+    {file = "attrs-21.2.0-py2.py3-none-any.whl", hash = "sha256:149e90d6d8ac20db7a955ad60cf0e6881a3f20d37096140088356da6c716b0b1"},
+    {file = "attrs-21.2.0.tar.gz", hash = "sha256:ef6aaac3ca6cd92904cdd0d83f629a15f18053ec84e6432106f7a4d04ae4f5fb"},
+]
+colorama = [
+    {file = "colorama-0.4.4-py2.py3-none-any.whl", hash = "sha256:9f47eda37229f68eee03b24b9748937c7dc3868f906e8ba69fbcbdd3bc5dc3e2"},
+    {file = "colorama-0.4.4.tar.gz", hash = "sha256:5941b2b48a20143d2267e95b1c2a7603ce057ee39fd88e7329b0c292aa16869b"},
+]
+importlib-metadata = [
+    {file = "importlib_metadata-4.8.1-py3-none-any.whl", hash = "sha256:b618b6d2d5ffa2f16add5697cf57a46c76a56229b0ed1c438322e4e95645bd15"},
+    {file = "importlib_metadata-4.8.1.tar.gz", hash = "sha256:f284b3e11256ad1e5d03ab86bb2ccd6f5339688ff17a4d797a0fe7df326f23b1"},
+]
+iniconfig = [
+    {file = "iniconfig-1.1.1-py2.py3-none-any.whl", hash = "sha256:011e24c64b7f47f6ebd835bb12a743f2fbe9a26d4cecaa7f53bc4f35ee9da8b3"},
+    {file = "iniconfig-1.1.1.tar.gz", hash = "sha256:bc3af051d7d14b2ee5ef9969666def0cd1a000e121eaea580d4a313df4b37f32"},
+]
+packaging = [
+    {file = "packaging-21.0-py3-none-any.whl", hash = "sha256:c86254f9220d55e31cc94d69bade760f0847da8000def4dfe1c6b872fd14ff14"},
+    {file = "packaging-21.0.tar.gz", hash = "sha256:7dc96269f53a4ccec5c0670940a4281106dd0bb343f47b7471f779df49c2fbe7"},
+]
+pluggy = [
+    {file = "pluggy-1.0.0-py2.py3-none-any.whl", hash = "sha256:74134bbf457f031a36d68416e1509f34bd5ccc019f0bcc952c7b909d06b37bd3"},
+    {file = "pluggy-1.0.0.tar.gz", hash = "sha256:4224373bacce55f955a878bf9cfa763c1e360858e330072059e10bad68531159"},
+]
+py = [
+    {file = "py-1.10.0-py2.py3-none-any.whl", hash = "sha256:3b80836aa6d1feeaa108e046da6423ab8f6ceda6468545ae8d02d9d58d18818a"},
+    {file = "py-1.10.0.tar.gz", hash = "sha256:21b81bda15b66ef5e1a777a21c4dcd9c20ad3efd0b3f817e7a809035269e1bd3"},
+]
+pyparsing = [
+    {file = "pyparsing-2.4.7-py2.py3-none-any.whl", hash = "sha256:ef9d7589ef3c200abe66653d3f1ab1033c3c419ae9b9bdb1240a85b024efc88b"},
+    {file = "pyparsing-2.4.7.tar.gz", hash = "sha256:c203ec8783bf771a155b207279b9bccb8dea02d8f0c9e5f8ead507bc3246ecc1"},
+]
+pytest = [
+    {file = "pytest-6.2.5-py3-none-any.whl", hash = "sha256:7310f8d27bc79ced999e760ca304d69f6ba6c6649c0b60fb0e04a4a77cacc134"},
+    {file = "pytest-6.2.5.tar.gz", hash = "sha256:131b36680866a76e6781d13f101efb86cf674ebb9762eb70d3082b6f29889e89"},
+]
+pytest-randomly = [
+    {file = "pytest-randomly-3.10.1.tar.gz", hash = "sha256:d4ef5dbf27e542e6a4e4cec7a20ef3f1b906bce21fa340ca5657b5326ef23a64"},
+    {file = "pytest_randomly-3.10.1-py3-none-any.whl", hash = "sha256:d28d490e3a743bdd64c5bc87c5fc182eac966ba6432c6bb6b224e32e76527e9e"},
+]
+toml = [
+    {file = "toml-0.10.2-py2.py3-none-any.whl", hash = "sha256:806143ae5bfb6a3c6e736a764057db0e6a0e05e338b5630894a5f779cabb4f9b"},
+    {file = "toml-0.10.2.tar.gz", hash = "sha256:b3bda1d108d5dd99f4a20d24d9c348e91c4db7ab1b749200bded2f839ccbe68f"},
+]
+zipp = [
+    {file = "zipp-3.5.0-py3-none-any.whl", hash = "sha256:957cfda87797e389580cb8b9e3870841ca991e2125350677b2ca83a0e99390a3"},
+    {file = "zipp-3.5.0.tar.gz", hash = "sha256:f5812b1e007e48cff63449a5e9f4e7ebea716b4111f9c4f9a645f91d579bf0c4"},
+]
diff --git a/tests/pytest-randomly/pyproject.toml b/tests/pytest-randomly/pyproject.toml
new file mode 100644
index 0000000..e1c988f
--- /dev/null
+++ b/tests/pytest-randomly/pyproject.toml
@@ -0,0 +1,13 @@
+[tool.poetry]
+name = "trivial"
+version = "0.1.0"
+description = "poetry2nix pytest-randomly test"
+authors = ["Your Name <you@example.com>"]
+
+[tool.poetry.dependencies]
+python = "^3.8"
+pytest-randomly = "^3.10.1"
+
+[build-system]
+requires = ["poetry>=0.12"]
+build-backend = "poetry.masonry.api"
diff --git a/tests/pytest-randomly/trivial/__init__.py b/tests/pytest-randomly/trivial/__init__.py
new file mode 100644
index 0000000..e69de29