diff --git a/.github/workflows/tox.yml b/.github/workflows/tox.yml
index 515094d..5c0458f 100644
--- a/.github/workflows/tox.yml
+++ b/.github/workflows/tox.yml
@@ -24,7 +24,6 @@ jobs:
         include:
           - tox_env: check-manifest
           - tox_env: lint
-          - tox_env: mypy
           - tox_env: py39
           - tox_env: py310
           - tox_env: py311
diff --git a/mypy.ini b/mypy.ini
index 6b958c4..b63cb2d 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,4 +1,5 @@
 [mypy]
+files = pdfss
 show_error_codes = true
 
 [mypy-pdfminer.*]
diff --git a/pyproject.toml b/pyproject.toml
index 0fb5f2b..6939360 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,6 +25,15 @@ dependencies = [
     "pdfminer.six",
 ]
 
+[project.optional-dependencies]
+test = [
+    "pytest",
+    "pytest-cov",
+]
+typing = [
+    "mypy",
+]
+
 [project.urls]
 Source = "https://github.com/lowatt/pdfss"
 Tracker = "https://github.com/lowatt/pdfss/issues"
diff --git a/tox.ini b/tox.ini
index 0fa0c89..8d612ba 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,13 +1,14 @@
 [tox]
 isolated_build = true
 envlist =
-  check-manifest,lint,py3,mypy
+  check-manifest,lint,py3
 
 [testenv]
-deps =
-  pytest
-  pytest-cov
+extras =
+  test
+  typing
 commands =
+  mypy
   {envpython} -m pytest {posargs:--cov pdfss --cov-report term --cov-fail-under 88}
 
 [testenv:lint]
@@ -34,10 +35,3 @@ deps =
   check-manifest
 commands =
   {envpython} -m check_manifest {toxinidir}
-
-
-[testenv:mypy]
-deps =
-  mypy
-commands =
-  {envpython} -m mypy pdfss