diff --git a/lib/classes/api/api_includes.inc.php b/lib/classes/api/api_includes.inc.php
index f7446b51..daea22b7 100644
--- a/lib/classes/api/api_includes.inc.php
+++ b/lib/classes/api/api_includes.inc.php
@@ -17,6 +17,32 @@
  */
 if (! defined('FROXLOR_INSTALL_DIR')) {
 	define('FROXLOR_INSTALL_DIR', dirname(dirname(dirname(__DIR__))));
+	// ensure that default timezone is set
+	if (function_exists("date_default_timezone_set") && function_exists("date_default_timezone_get")) {
+		@date_default_timezone_set(@date_default_timezone_get());
+	}
+	$installed = true;
+	// check whether the userdata file exists
+	if (! @file_exists(FROXLOR_INSTALL_DIR . '/lib/userdata.inc.php')) {
+		$installed = false;
+	}
+	// check whether we can read the userdata file
+	if ($installed && ! @is_readable(FROXLOR_INSTALL_DIR . '/lib/userdata.inc.php')) {
+		$installed = false;
+	}
+	if ($installed) {
+		// include userdata for content-check
+		require FROXLOR_INSTALL_DIR . '/lib/userdata.inc.php';
+		if (! isset($sql) || ! is_array($sql)) {
+			$installed = false;
+		}
+	}
+	// do not try to do anything if we have no installed/configured froxlor
+	if (! $installed) {
+		header("Status: 404 Not found", 404);
+		header($_SERVER["SERVER_PROTOCOL"] . " 404 Not found", 404);
+		exit();
+	}
 	require_once FROXLOR_INSTALL_DIR . '/lib/tables.inc.php';
 	require_once FROXLOR_INSTALL_DIR . '/lib/functions.php';
 }