diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index dd453758..f8a22da3 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -84,7 +84,7 @@ jobs:
     # there's some overlap with publish-pages.yml, but this one runs on pull
     # requests, doesn't publish, and runs more doc checks
     name: docs
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     steps:
       - name: Git clone
diff --git a/requirements-min.txt b/requirements-min.txt
index c46475b6..5cf3e824 100644
--- a/requirements-min.txt
+++ b/requirements-min.txt
@@ -4,3 +4,4 @@ requests == 2.20.0
 dnspython == 2.0.0
 # optional:
 argcomplete == 1.8.1
+pdfminer.six == 20181108
diff --git a/requirements.txt b/requirements.txt
index 9e70249d..c869cc03 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,3 +4,4 @@ requests >= 2.20
 dnspython >= 2.0
 # optional:
 argcomplete >= 1.8.1
+pdfminer.six >= 20181108
diff --git a/tox.ini b/tox.ini
index c4a414a9..eff1a51c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,7 +5,6 @@ envlist = py3{7,8,9,10,11}, minreqs
 deps =
     pyftpdlib
     parameterized
-    pdfminer.six
     pyopenssl
     pytest-xdist
     pytest-cov