diff --git a/includes/Admin/Admin.php b/includes/Admin/Admin.php
index 1146cad..d05c303 100644
--- a/includes/Admin/Admin.php
+++ b/includes/Admin/Admin.php
@@ -1377,6 +1377,7 @@ class Admin {
 								<th scope='row'><?php echo esc_html__( 'Position', KGVVM_TEXT_DOMAIN ); ?></th>
 								<td>
 									<label>
+										<input type='hidden' name='is_mandatory' value='0' />
 										<input type='checkbox' name='is_mandatory' value='1' <?php checked( $cost ? (bool) $cost->is_mandatory : true, true ); ?> />
 										<?php echo esc_html__( 'Verpflichtende Position', KGVVM_TEXT_DOMAIN ); ?>
 									</label>
diff --git a/includes/Validator.php b/includes/Validator.php
index f0c1d02..049ed80 100644
--- a/includes/Validator.php
+++ b/includes/Validator.php
@@ -259,7 +259,7 @@ class Validator {
 		$unit_amount       = isset( $data['unit_amount'] ) ? str_replace( ',', '.', wp_unslash( $data['unit_amount'] ) ) : '';
 		$entry_year        = $this->sanitize_cost_year( $data );
 		$distribution_type = sanitize_key( wp_unslash( isset( $data['distribution_type'] ) ? $data['distribution_type'] : 'parcel' ) );
-		$is_mandatory       = isset( $data['is_mandatory'] ) ? (bool) $data['is_mandatory'] : true;
+		$is_mandatory      = isset( $data['is_mandatory'] ) && '1' === (string) wp_unslash( $data['is_mandatory'] );
 
 		return array(
 			'entry_year'        => $entry_year,