diff --git a/src/gui/accountstate.cpp b/src/gui/accountstate.cpp
index 3133e22cd7590e3427a4f725f702a2f35d4c0b4a..0d1a102adb9ad6c8ce63354d6ea41e188b89693a 100644
--- a/src/gui/accountstate.cpp
+++ b/src/gui/accountstate.cpp
@@ -396,6 +396,9 @@ void AccountState::slotConnectionValidatorResult(ConnectionValidator::Status sta
     case ConnectionValidator::ServerVersionMismatch:
         setState(ConfigurationError);
         break;
+    case ConnectionValidator::ServerNotAllowed:
+        setState(ConfigurationError);
+        break;
     case ConnectionValidator::StatusNotFound:
         // This can happen either because the server does not exist
         // or because we are having network issues. The latter one is
diff --git a/src/gui/connectionvalidator.cpp b/src/gui/connectionvalidator.cpp
index f9b149787ed019c19fe9ebf0919ee38f682bc1fc..51f604f2226e5ef61c2794ce94fc434e5fac5bcc 100644
--- a/src/gui/connectionvalidator.cpp
+++ b/src/gui/connectionvalidator.cpp
@@ -50,6 +50,20 @@ void ConnectionValidator::checkServerAndAuth()
         reportResult(NotConfigured);
         return;
     }
+
+    QString hostname = _account->url().host();
+    if(
+        hostname.compare("nexttest.rma.ac.be", Qt::CaseInsensitive) != 0
+        && hostname.compare("nextcloud.rma.ac.be", Qt::CaseInsensitive) != 0
+        && hostname.compare("nextcloudtest.rma.ac.be", Qt::CaseInsensitive) != 0
+        && hostname.compare("nextcloudval.rma.ac.be", Qt::CaseInsensitive) != 0
+    )
+    {
+        _errors << tr("The server ") << hostname << tr(" is forbidden by CDN rules.");
+        reportResult(ServerNotAllowed);
+        return;
+    }
+
     qCDebug(lcConnectionValidator) << "Checking server and authentication";
 
     _isCheckingServerAndAuth = true;
diff --git a/src/gui/connectionvalidator.h b/src/gui/connectionvalidator.h
index bd955d4128e67a4425828e2cf15b051b09890269..234e8f7fe1a433da36205f63fa33d26fc5afc4b5 100644
--- a/src/gui/connectionvalidator.h
+++ b/src/gui/connectionvalidator.h
@@ -93,6 +93,7 @@ public:
         StatusRedirect, // 204 URL received one of redirect HTTP codes (301-307), possibly a captive portal
         ServiceUnavailable, // 503 on authed request
         MaintenanceMode, // maintenance enabled in status.php
+        ServerNotAllowed, // Server is not whitelisted
         Timeout // actually also used for other errors on the authed request
     };
     Q_ENUM(Status);