diff --git a/application/controllers/api/frontend/v1/ClassScheduleApi.php b/application/controllers/api/frontend/v1/ClassScheduleApi.php
index 2402cb5fc..3f6c3a8ae 100644
--- a/application/controllers/api/frontend/v1/ClassScheduleApi.php
+++ b/application/controllers/api/frontend/v1/ClassScheduleApi.php
@@ -240,8 +240,8 @@ class ClassScheduleApi extends FHCAPI_Controller
 	public function deleteClassTimeSlotValidityPeriod($classTimeSlotValidityPeriodId)
 	{
 		$validityPeriodResult = $this->ClassTimeSlotValidityPeriodModel->loadWhere(['unterrichtszeitengueltigkeit_id' => $classTimeSlotValidityPeriodId]);
-		$validityPeriodResult = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
-		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriodResult->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
+		$validityPeriod = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
+		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriod->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
 			$this->terminateWithError($this->p->t('ui', 'keineBerechtigung'));
 		}
 
@@ -265,8 +265,8 @@ class ClassScheduleApi extends FHCAPI_Controller
 	public function getClassTimeSlotsForValidityPeriod($classTimeSlotValidityPeriodId)
 	{
 		$validityPeriodResult = $this->ClassTimeSlotValidityPeriodModel->loadWhere(['unterrichtszeitengueltigkeit_id' => $classTimeSlotValidityPeriodId]);
-		$validityPeriodResult = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
-		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriodResult->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
+		$validityPeriod = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
+		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriod->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
 			$this->terminateWithError($this->p->t('ui', 'keineBerechtigung'));
 		}
 
@@ -282,8 +282,8 @@ class ClassScheduleApi extends FHCAPI_Controller
 		if($this->form_validation->run() == FALSE) $this->terminateWithValidationErrors($this->form_validation->error_array());
 
 		$validityPeriodResult = $this->ClassTimeSlotValidityPeriodModel->loadWhere(['unterrichtszeitengueltigkeit_id' => $classTimeSlotValidityPeriodId]);
-		$validityPeriodResult = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
-		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriodResult->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
+		$validityPeriod = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
+		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriod->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
 			$this->terminateWithError($this->p->t('ui', 'keineBerechtigung'));
 		}
 
@@ -318,8 +318,8 @@ class ClassScheduleApi extends FHCAPI_Controller
 		if($this->form_validation->run() == FALSE) $this->terminateWithValidationErrors($this->form_validation->error_array());
 
 		$validityPeriodResult = $this->ClassTimeSlotValidityPeriodModel->loadWhere(['unterrichtszeitengueltigkeit_id' => $classTimeSlotValidityPeriodId]);
-		$validityPeriodResult = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
-		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriodResult->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
+		$validityPeriod = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
+		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriod->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
 			$this->terminateWithError($this->p->t('ui', 'keineBerechtigung'));
 		}
 
@@ -357,8 +357,8 @@ class ClassScheduleApi extends FHCAPI_Controller
 	public function deleteClassTimeSlotsForValidityPeriodPerGroup($classTimeSlotValidityPeriodId, $groupIdentifikator)
 	{
 		$validityPeriodResult = $this->ClassTimeSlotValidityPeriodModel->loadWhere(['unterrichtszeitengueltigkeit_id' => $classTimeSlotValidityPeriodId]);
-		$validityPeriodResult = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
-		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriodResult->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
+		$validityPeriod = $this->getDataOrTerminateWithError($validityPeriodResult)[0];
+		if (!$this->isUserEntitledForOrganizationalUnit($validityPeriod->oe_kurzbz, 'lehre/unterrichtszeiten_gk')) {
 			$this->terminateWithError($this->p->t('ui', 'keineBerechtigung'));
 		}
 		
@@ -460,9 +460,27 @@ class ClassScheduleApi extends FHCAPI_Controller
 	
 	public function deleteClassTimeSlotType($classTimeSlotTypeId)
 	{
+		$isClassTimeSlotDeletable = true;
+
+		$validityPeriodResult = $this->ClassTimeSlotValidityPeriodModel->loadWhere(['unterrichtszeitentyp_kurzbz' => $classTimeSlotTypeId]);
+		$validityPeriod = $this->getDataOrTerminateWithError($validityPeriodResult);
+		if ($validityPeriod && count($validityPeriod) > 0) {
+			$isClassTimeSlotDeletable = false;
+		}
+
+		$classTimeSlotResult = $this->ClassTimeSlotModel->loadWhere(['unterrichtszeitentyp_kurzbz' => $classTimeSlotTypeId]);
+		$classTimeSlot = $this->getDataOrTerminateWithError($classTimeSlotResult);
+		if ($classTimeSlot && count($classTimeSlot) > 0) {
+			$isClassTimeSlotDeletable = false;
+		}
+
 		$this->db->trans_start();
 
-		$result = $this->ClassTimeSlotTypeModel->delete(['unterrichtszeitentyp_kurzbz' => $classTimeSlotTypeId]);
+		if (!$isClassTimeSlotDeletable) {
+			$result = $this->ClassTimeSlotTypeModel->update($classTimeSlotTypeId, ['aktiv' => false, 'updateamum' => date('c'), 'updatevon' => getAuthUid()]);
+		} else {
+			$result = $this->ClassTimeSlotTypeModel->delete(['unterrichtszeitentyp_kurzbz' => $classTimeSlotTypeId]);
+		}
 		if (isError($result)) {
 			$this->terminateWithError(getError($result), self::ERROR_TYPE_GENERAL);
 		}
diff --git a/application/models/education/ClassTimeSlotType_model.php b/application/models/education/ClassTimeSlotType_model.php
index 31cb87d69..0000bb35e 100644
--- a/application/models/education/ClassTimeSlotType_model.php
+++ b/application/models/education/ClassTimeSlotType_model.php
@@ -9,7 +9,7 @@ class ClassTimeSlotType_model extends DB_Model
 	{
 		parent::__construct();
 		$this->dbTable = 'lehre.tbl_unterrichtszeiten_typ';
-		$this->pk = 'unterrichtszeit_id';
+		$this->pk = 'unterrichtszeitentyp_kurzbz';
 	}
 
 }