diff --git a/plinth/modules/roundcube/__init__.py b/plinth/modules/roundcube/__init__.py
index 5c1ef8cf0..7c5295154 100644
--- a/plinth/modules/roundcube/__init__.py
+++ b/plinth/modules/roundcube/__init__.py
@@ -39,3 +39,13 @@ def init():
 def is_enabled():
     """Return whether the module is enabled."""
     return action_utils.webserver_is_enabled('roundcube')
+
+
+def diagnose():
+    """Run diagnostics and return the results."""
+    results = []
+
+    results.extend(action_utils.diagnose_url_on_all(
+        'https://{host}/roundcube', extra_options=['--no-check-certificate']))
+
+    return results
diff --git a/plinth/modules/roundcube/templates/roundcube.html b/plinth/modules/roundcube/templates/roundcube.html
index 7b47dbaab..28e2a2088 100644
--- a/plinth/modules/roundcube/templates/roundcube.html
+++ b/plinth/modules/roundcube/templates/roundcube.html
@@ -43,6 +43,7 @@
   (<a href="https://www.google.com/settings/security/lesssecureapps"
   >https://www.google.com/settings/security/lesssecureapps</a>).</p>
 
+{% include "diagnostics_button.html" with module="roundcube" %}
 
 <h3>Configuration</h3>