diff --git a/application/controllers/api/frontend/v1/studstatus/Unterbrechung.php b/application/controllers/api/frontend/v1/studstatus/Unterbrechung.php
index abf58cf4f..72d5dbccc 100644
--- a/application/controllers/api/frontend/v1/studstatus/Unterbrechung.php
+++ b/application/controllers/api/frontend/v1/studstatus/Unterbrechung.php
@@ -127,9 +127,9 @@ class Unterbrechung extends FHCAPI_Controller
 		$this->form_validation->set_rules(
 			'datum_wiedereinstieg',
 			'Datum Wiedereinstieg',
-			'required|callback_isValidDate|callback_isDateInFuture',
+			'required|is_valid_date|callback_isDateInFuture',
 			[
-				'isValidDate' => $this->p->t('ui', 'error_invalid_date'),
+				'is_valid_date' => $this->p->t('ui', 'error_invalid_date'),
 				'isDateInFuture' => $this->p->t('ui', 'error_invalid_date')
 			]
 		);
@@ -209,18 +209,9 @@ class Unterbrechung extends FHCAPI_Controller
 		$this->terminateWithSuccess(getData($result));
 	}
 
-	public function isValidDate($date)
-	{
-		try {
-		    new DateTime($date);
-		} catch (Exception $e) {
-			return false;
-		}
-		return true;
-	}
-
 	public function isDateInFuture($date)
 	{
 		return new DateTime() < new DateTime($date);
 	}
 }
+
diff --git a/application/controllers/api/frontend/v1/stv/Student.php b/application/controllers/api/frontend/v1/stv/Student.php
index 2721bbd6f..2fb354f0c 100644
--- a/application/controllers/api/frontend/v1/stv/Student.php
+++ b/application/controllers/api/frontend/v1/stv/Student.php
@@ -542,6 +542,7 @@ class Student extends FHCAPI_Controller
 
 		$this->_validate();
 
+		// TODO(chris): This should be in a library
 		$this->load->model('crm/Student_model', 'StudentModel');
 		$this->load->model('crm/Prestudent_model', 'PrestudentModel');
 		$this->load->model('crm/Prestudentstatus_model', 'PrestudentstatusModel');
@@ -793,8 +794,8 @@ class Student extends FHCAPI_Controller
 		$this->form_validation->set_rules('geschlecht', 'Geschlecht', 'callback_requiredIfNotPersonId', [
 			'requiredIfNotPersonId' => $this->p->t('ui', 'error_fieldRequired', ['field' => $this->p->t('person', 'geschlecht')])
 		]);
-		$this->form_validation->set_rules('gebdatum', 'Geburtsdatum', ['isValidDate', function($value) { return isValidDate($value); }], [
-			'isValidDate' => $this->p->t('ui', 'error_invalid_date')
+		$this->form_validation->set_rules('gebdatum', 'Geburtsdatum', 'is_valid_date', [
+			'is_valid_date' => $this->p->t('ui', 'error_invalid_date')
 		]);
 		//$this->form_validation->set_rules('address[checked]', 'Address', 'required');
 		$this->form_validation->set_rules('address[plz]', 'PLZ', 'callback_requiredIfAddressFunc', [
diff --git a/application/helpers/hlp_common_helper.php b/application/helpers/hlp_common_helper.php
index b13d9d44d..51d520a80 100644
--- a/application/helpers/hlp_common_helper.php
+++ b/application/helpers/hlp_common_helper.php
@@ -408,22 +408,6 @@ function findResource($path, $resource, $subdir = false, $extraDir = null)
 	return null;
 }
 
-/**
- * check if String can be converted to a date
- */
-function isValidDate($dateString)
-{
-	try
-	{
-		return (new DateTime($dateString)) !== false;
-	}
-	catch(Exception $e)
-	{
-		return false;
-	}
-}
-
-
 // ------------------------------------------------------------------------
 // PHP functions that don't exist in older versions
 // ------------------------------------------------------------------------
@@ -446,7 +430,8 @@ if (!function_exists('array_is_list')) {
 // ------------------------------------------------------------------------
 
 /**
- * check if string can be converted to a date
+ * Check if the provided parameter is a string containing a valid date
+ * NOTE: the name is in the "snake case" format because othewise the CI form validation _cannot_ use it
  */
 function is_valid_date($dateString)
 {