diff --git a/.github/workflows/unittest.yml b/.github/workflows/unittest.yml
index 41c7aa33..9212441e 100644
--- a/.github/workflows/unittest.yml
+++ b/.github/workflows/unittest.yml
@@ -12,7 +12,7 @@ jobs:
       with:
         python-version: ${{ matrix.python }}
     - name: install tox
-      run: pip install tox
+      run: pip install 'virtualenv<20.22.0' 'tox<4.5.0'
     - name: add mandatory git remote
       run: git remote add hpcugent https://github.com/hpcugent/vsc-base.git
     - name: Run tox
diff --git a/lib/vsc/utils/mail.py b/lib/vsc/utils/mail.py
index 9e304b34..7883e914 100644
--- a/lib/vsc/utils/mail.py
+++ b/lib/vsc/utils/mail.py
@@ -321,7 +321,7 @@ def sendHTMLMail(
 
         # Record the MIME types of both parts - text/plain and text/html_message.
         msg_plain = MIMEText(text_alternative, 'plain', 'utf-8')
-        msg_html = MIMEText(html_message, 'html_message', 'utf-8')
+        msg_html = MIMEText(html_message, "html", 'utf-8')
 
         # Attach parts into message container.
         # According to RFC 2046, the last part of a multipart message, in this case
diff --git a/setup.py b/setup.py
index 11676c79..785eb0ec 100755
--- a/setup.py
+++ b/setup.py
@@ -37,7 +37,7 @@
 from vsc.install.shared_setup import ag, kh, jt, sdw
 
 PACKAGE = {
-    'version': '3.5.3',
+    'version': '3.5.4',
     'author': [sdw, jt, ag, kh],
     'maintainer': [sdw, jt, ag, kh],
     'install_requires': [