diff --git a/Dockerfile b/Dockerfile
index daff725..e13c5f1 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -21,7 +21,7 @@ ENV PATH="$VIRTUAL_ENV/bin:$PATH"
 # lxml - required for previews
 RUN pip install --upgrade pip && \
     pip install --upgrade setuptools && \
-    pip install matrix-synapse==${VERSION} psycopg2-binary python-ldap matrix-synapse-ldap3 lxml
+    pip install matrix-synapse==${VERSION} psycopg2-binary python-ldap matrix-synapse-ldap3 lxml publicsuffix2
 
 RUN curl -sL https://github.com/mikefarah/yq/releases/download/3.2.1/yq_linux_amd64 -o /usr/bin/yq && \
     chmod +x /usr/bin/yq
diff --git a/start.sh b/start.sh
index 9f9761e..26f2c22 100755
--- a/start.sh
+++ b/start.sh
@@ -23,11 +23,14 @@ if [[ ! -f /app/data/configs/homeserver.yaml ]]; then
 
     mv /app/data/configs/${CLOUDRON_APP_DOMAIN}.signing.key /app/data/configs/signing.key
 
+    # this is set at installation time and not changed after
+    server_name=$(python -c "from publicsuffix2 import get_sld; print(get_sld('${CLOUDRON_APP_DOMAIN}'));")
+    yq w -i /app/data/configs/homeserver.yaml server_name "${CLOUDRON_APP_DOMAIN}"
+
     yq w -i /app/data/configs/homeserver.yaml registration_shared_secret "$(pwgen -1s 64)"
 fi
 
 echo "==> Configuring synapse"
-yq w -i /app/data/configs/homeserver.yaml server_name "${CLOUDRON_APP_DOMAIN}"
 yq w -i /app/data/configs/homeserver.yaml public_baseurl "${CLOUDRON_APP_ORIGIN}"
 
 # tls