diff --git a/core/ajax/update.php b/core/ajax/update.php
index 6015a901eb..db00da0223 100644
--- a/core/ajax/update.php
+++ b/core/ajax/update.php
@@ -5,11 +5,15 @@ require_once '../../lib/base.php';
 
 if (OC::checkUpgrade(false)) {
 	\OC_DB::enableCaching(false);
+	OC_Config::setValue('maintenance', true);
+	$installedVersion = OC_Config::getValue('version', '0.0.0');
+	$currentVersion = implode('.', OC_Util::getVersion());
+	OC_Log::write('core', 'starting upgrade from ' . $installedVersion . ' to ' . $currentVersion, OC_Log::WARN);
 	$updateEventSource = new OC_EventSource();
 	$watcher = new UpdateWatcher($updateEventSource);
 	OC_Hook::connect('update', 'success', $watcher, 'success');
 	OC_Hook::connect('update', 'error', $watcher, 'error');
-	OC_Hook::connect('update', 'error', $watcher, 'failure');
+	OC_Hook::connect('update', 'failure', $watcher, 'failure');
 	$watcher->success('Turned on maintenance mode');
 	try {
 		$result = OC_DB::updateDbFromStructure(OC::$SERVERROOT.'/db_structure.xml');
@@ -99,6 +103,7 @@ class UpdateWatcher {
 		OC_Util::obEnd();
 		$this->eventSource->send('failure', $message);
 		$this->eventSource->close();
+		OC_Config::setValue('maintenance', false);
 		die();
 	}
 
@@ -108,4 +113,4 @@ class UpdateWatcher {
 		$this->eventSource->close();
 	}
 
-}
+}
\ No newline at end of file
diff --git a/lib/base.php b/lib/base.php
index a6e4a47dbf..26e9595e86 100644
--- a/lib/base.php
+++ b/lib/base.php
@@ -235,10 +235,7 @@ class OC {
 			$currentVersion = implode('.', OC_Util::getVersion());
 			if (version_compare($currentVersion, $installedVersion, '>')) {
 				if ($showTemplate && !OC_Config::getValue('maintenance', false)) {
-					OC_Config::setValue('maintenance', true);
-					OC_Log::write('core',
-						'starting upgrade from ' . $installedVersion . ' to ' . $currentVersion,
-						OC_Log::WARN);
+					OC_Config::setValue('theme', '');
 					$minimizerCSS = new OC_Minimizer_CSS();
 					$minimizerCSS->clearCache();
 					$minimizerJS = new OC_Minimizer_JS();
diff --git a/lib/config.php b/lib/config.php
index 9b87d4ce4e..3cbb89fb98 100644
--- a/lib/config.php
+++ b/lib/config.php
@@ -187,7 +187,7 @@ class OC_Config{
 		}
 		// Prevent others not to read the config
 		@chmod($filename, 0640);
-
+		OC_Util::clearOpcodeCache();
 		return true;
 	}
 }
diff --git a/lib/connector/sabre/maintenanceplugin.php b/lib/connector/sabre/maintenanceplugin.php
index 329fa4443a..2eda269afc 100644
--- a/lib/connector/sabre/maintenanceplugin.php
+++ b/lib/connector/sabre/maintenanceplugin.php
@@ -50,6 +50,9 @@ class OC_Connector_Sabre_MaintenancePlugin extends Sabre_DAV_ServerPlugin
 		if (OC_Config::getValue('maintenance', false)) {
 			throw new Sabre_DAV_Exception_ServiceUnavailable();
 		}
+		if (OC::checkUpgrade(false)) {
+			throw new Sabre_DAV_Exception_ServiceUnavailable('Upgrade needed');
+		}
 
 		return true;
 	}
diff --git a/lib/util.php b/lib/util.php
index 95af22ed0e..ddef0c63c5 100755
--- a/lib/util.php
+++ b/lib/util.php
@@ -832,6 +832,26 @@ class OC_Util {
 		return $theme;
 	}
 
+	/**
+	 * Clear the opcode cache if one exists
+	 * This is necessary for writing to the config file
+	 * in case the opcode cache doesn't revalidate files
+	 */
+	public static function clearOpcodeCache() {
+		// APC
+		if (function_exists('apc_clear_cache')) {
+			apc_clear_cache();
+		}
+		// Zend Opcache
+		if (function_exists('accelerator_reset')) {
+			accelerator_reset();
+		}
+		// XCache
+		if (function_exists('xcache_clear_cache')) {
+			xcache_clear_cache(XC_TYPE_VAR, 0);
+		}
+	}
+
 	/**
 	 * Normalize a unicode string
 	 * @param string $value a not normalized string