diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 297562c..161d18c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -43,6 +43,10 @@ jobs:
       - name: Install Hatch
         run: |
           pip install hatch
+      - name: Pin virtualenv for Python 3.9
+        if: matrix.python == '3.9'
+        run: |
+          pip install 'virtualenv<21'
       - name: Install dependencies
         run: |
           hatch run test:pip freeze
diff --git a/pyproject.toml b/pyproject.toml
index 65f6a3b..d5d7c2e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -32,7 +32,7 @@ classifiers = [
 dynamic = ["version"]
 requires-python = ">=3.9"
 dependencies = [
-    "mkdocs >=1.1.1",
+    "mkdocs >=1.4.0",
     #min "jinja2 >=2.10.1",
     #min "markupsafe >=2.0.1",
 ]