diff --git a/ucs-school-umc-installer/umc/python/schoolinstaller/__init__.py b/ucs-school-umc-installer/umc/python/schoolinstaller/__init__.py
index a8ecda1..0ac0ec9 100644
--- a/ucs-school-umc-installer/umc/python/schoolinstaller/__init__.py
+++ b/ucs-school-umc-installer/umc/python/schoolinstaller/__init__.py
@@ -45,6 +45,7 @@
 import select
 import errno
 from httplib import HTTPException
+from distutils.version import LooseVersion
 
 import notifier
 import notifier.threads
@@ -352,7 +353,7 @@ def get_samba_version(self):
 			return 3
 		return None
 
-	def get_ucs_school_version(self):
+	def get_ucs_school_environment(self):
 		'''Returns 'singlemaster', 'multiserver', or None'''
 		if self.package_manager.is_installed('ucs-school-singlemaster'):
 			return 'singlemaster'
@@ -360,6 +361,9 @@ def get_ucs_school_version(self):
 			return 'multiserver'
 		return None
 
+	def get_school_version(self):
+		return ucr.get('appcenter/apps/ucsschool/version')
+
 	@simple_response
 	def query(self, **kwargs):
 		"""Returns a dictionary of initial values for the form."""
@@ -369,7 +373,7 @@ def query(self, **kwargs):
 			'server_role': ucr.get('server/role'),
 			'joined': os.path.exists('/var/univention-join/joined'),
 			'samba': self.get_samba_version(),
-			'ucsschool': self.get_ucs_school_version(),
+			'ucsschool': self.get_ucs_school_environment(),
 			'guessed_master': get_master_dns_lookup(),
 			'hostname': ucr.get('hostname'),
 		}
@@ -451,18 +455,19 @@ def _get_schoolinfo(self, school_ou):
 			educational_slaves = [SchoolDCSlave.from_dn(dn, None, lo).name for dn in school.educational_servers]
 			administrative_slaves = [SchoolDCSlave.from_dn(dn, None, lo).name for dn in school.administrative_servers]
 
-		school_version = None
+		school_environment = None
 		for package, version in (('ucs-school-singlemaster', 'singlemaster'), ('ucs-school-slave', 'multiserver'), ('ucs-school-master', 'multiserver')):
 			package = self.package_manager.get_package(package)
 			if package and package.is_installed:
-				school_version = version
+				school_environment = version
 				break
 
 		return {
 			'exists': exists,
 			'school': school_ou,
 			'samba': self.get_samba_version(),
-			'school_version': school_version,
+			'school_version': school_environment,
+			'school_app_version': self.get_school_version(),
 			'classShareServer': class_share_server,
 			'homeShareServer': home_share_server,
 			'educational_slaves': educational_slaves,
@@ -533,16 +538,23 @@ def install(self, request):
 			# check for a compatible environment on the DC master
 
 			schoolinfo = self._get_schoolinfo_from_master(username, password, master, school_ou)
-			school_version = schoolinfo['school_version']
-			if not school_version:
+			school_environment = schoolinfo['school_version']
+			if not school_environment:
 				raise SchoolInstallerError(_('Please install UCS@school on the master domain controller system. Cannot proceed installation on this system.'))
-			if server_role == 'domaincontroller_slave' and school_version != 'multiserver':
+			if server_role == 'domaincontroller_slave' and school_environment != 'multiserver':
 				raise SchoolInstallerError(_('The master domain controller is not configured for a UCS@school multi server environment. Cannot proceed installation on this system.'))
-			if server_role == 'domaincontroller_backup' and school_version != setup:
+			if server_role == 'domaincontroller_backup' and school_environment != setup:
 				raise SchoolInstallerError(_('The UCS@school master domain controller needs to be configured similarly to this backup system. Please choose the correct environment type for this system.'))
 			if server_role == 'domaincontroller_backup' and not joined:
 				raise SchoolInstallerError(_('In order to install UCS@school on a backup domain controller, the system needs to be joined first.'))
 
+			school_version = schoolinfo.get('school_app_version')
+			local_school_version = self.get_school_version()
+			if not school_version or LooseVersion(school_version) < LooseVersion(local_school_version):
+				if not ucr.is_true('ucsschool/join/ignore-version-mismatch/%s/%s' % (school_version, local_school_version)):
+					raise SchoolInstallerError(_('The version of the UCS@school app on the DC master is lower than the version on this host. Please consult the Univention Support Database on how to proceed: http://sdb.univention.de/1373'))
+				MODULE.warn('Ignoring UCS@school version mismatch: Master: %s; Local: %s;' % (school_version, local_school_version))
+
 		# everything ok, try to acquire the lock for the package installation
 		lock_aquired = self.package_manager.lock(raise_on_fail=False)
 		if not lock_aquired: