diff --git a/plinth/modules/config/tests/config.feature b/plinth/modules/config/tests/config.feature
index eb90d751c..c18103011 100644
--- a/plinth/modules/config/tests/config.feature
+++ b/plinth/modules/config/tests/config.feature
@@ -15,6 +15,10 @@ Scenario: Change domain name
   When I change the domain name to mydomain.example
   Then the domain name should be mydomain.example
 
+Scenario: Capitalized domain name
+  When I change the domain name to Mydomain.example
+  Then the domain name should be mydomain.example
+
 Scenario: Change webserver home page
   Given the syncthing application is installed
   And the syncthing application is enabled
diff --git a/plinth/modules/config/views.py b/plinth/modules/config/views.py
index abc89095b..a88a6cde2 100644
--- a/plinth/modules/config/views.py
+++ b/plinth/modules/config/views.py
@@ -120,6 +120,10 @@ def set_domainname(domainname, old_domainname):
     # Domain name should be ASCII. If it's unicode, convert to ASCII.
     domainname = str(domainname)
 
+    # Domain name is not case sensitive, but Let's Encrypt certificate
+    # paths use lower-case domain name.
+    domainname = domainname.lower()
+
     LOGGER.info('Changing domain name to - %s', domainname)
     actions.superuser_run('domainname-change', [domainname])