diff --git a/src/mail.js b/src/mail.js
index 5b5663592..99c9e5d27 100644
--- a/src/mail.js
+++ b/src/mail.js
@@ -556,7 +556,7 @@ function restartMail(callback) {
     const cloudronToken = hat(8 * 128);
 
     // admin and mail share the same certificate
-    reverseProxy.getCertificate({ fqdn: config.adminFqdn(), domain: config.adminDomain() }, function (error, bundle) {
+    reverseProxy.getCertificate(config.adminFqdn(), config.adminDomain(), function (error, bundle) {
         if (error) return callback(error);
 
         // the setup script copies dhparams.pem to /addons/mail
diff --git a/src/reverseproxy.js b/src/reverseproxy.js
index bfbccd0b7..6895fb204 100644
--- a/src/reverseproxy.js
+++ b/src/reverseproxy.js
@@ -316,17 +316,18 @@ function getCertificateByHostname(hostname, domainObject, callback) {
     callback(null);
 }
 
-function getCertificate(app, callback) {
-    assert.strictEqual(typeof app, 'object');
+function getCertificate(fqdn, domain, callback) {
+    assert.strictEqual(typeof fqdn, 'string');
+    assert.strictEqual(typeof domain, 'string');
     assert.strictEqual(typeof callback, 'function');
 
-    domains.get(app.domain, function (error, domainObject) {
+    domains.get(domain, function (error, domainObject) {
         if (error) return callback(error);
 
-        getCertificateByHostname(app.fqdn, domainObject, function (error, result) {
+        getCertificateByHostname(fqdn, domainObject, function (error, result) {
             if (error || result) return callback(error, result);
 
-            return getFallbackCertificate(app.domain, callback);
+            return getFallbackCertificate(domain, callback);
         });
     });
 }
@@ -430,7 +431,7 @@ function writeAdminConfig(domain, callback) {
 
         const adminFqdn = domains.fqdn(constants.ADMIN_LOCATION, domainObject);
 
-        getCertificate({ fqdn: adminFqdn, domain: domainObject.domain }, function (error, bundle) {
+        getCertificate(adminFqdn, domainObject.domain, function (error, bundle) {
             if (error) return callback(error);
 
             writeAdminNginxConfig(bundle, `${adminFqdn}.conf`, adminFqdn, callback);