diff --git a/src/MDCurrenciesSet.php b/src/MDCurrenciesSet.php
index 6d93204..bd771d7 100644
--- a/src/MDCurrenciesSet.php
+++ b/src/MDCurrenciesSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available currencies.
  */
-class MDCurrenciesSet extends MDValueSet {
+final class MDCurrenciesSet extends MDValueSet {
 
     const CURRENCIES = [
         '',
diff --git a/src/MDEntryTypesSet.php b/src/MDEntryTypesSet.php
index 5d7a458..70b17ad 100644
--- a/src/MDEntryTypesSet.php
+++ b/src/MDEntryTypesSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available marking types.
  */
-class MDEntryTypesSet extends MDValueSet {
+final class MDEntryTypesSet extends MDValueSet {
 
     const ENTRY_TYPES = [
         '0', //
diff --git a/src/MDEventsSet.php b/src/MDEventsSet.php
index 71922dd..9ea00fe 100644
--- a/src/MDEventsSet.php
+++ b/src/MDEventsSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available units for events.
  */
-class MDEventsSet extends MDValueSet {
+final class MDEventsSet extends MDValueSet {
 
     const EVENT_IDS = [
         '1',  // => Created
diff --git a/src/MDLanguagesSet.php b/src/MDLanguagesSet.php
index 416d68a..7686e52 100644
--- a/src/MDLanguagesSet.php
+++ b/src/MDLanguagesSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing static functions for getting available languages.
  */
-class MDLanguagesSet {
+final class MDLanguagesSet {
 
     const AVAILABLE_LANGUAGES = [
         'aa' => 'Afar-áf',
diff --git a/src/MDLicensesSet.php b/src/MDLicensesSet.php
index 31a0b98..7460546 100644
--- a/src/MDLicensesSet.php
+++ b/src/MDLicensesSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing static functions for getting available licenses on md.
  */
-class MDLicensesSet extends MDValueSet {
+final class MDLicensesSet extends MDValueSet {
 
     const AVAILABLE_LICENSES = [
 
diff --git a/src/MDMarkingTypesSet.php b/src/MDMarkingTypesSet.php
index 6500b0b..033b242 100644
--- a/src/MDMarkingTypesSet.php
+++ b/src/MDMarkingTypesSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available marking types.
  */
-class MDMarkingTypesSet extends MDValueSet {
+final class MDMarkingTypesSet extends MDValueSet {
 
     const MARKING_TYPES = [
         'signature',
diff --git a/src/MDObjectPositionsSet.php b/src/MDObjectPositionsSet.php
index 72ae2ef..571b906 100644
--- a/src/MDObjectPositionsSet.php
+++ b/src/MDObjectPositionsSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available positions on an object.
  */
-class MDObjectPositionsSet extends MDValueSet {
+final class MDObjectPositionsSet extends MDValueSet {
 
     const POSITIONS = [
         'left', 'top_left', 'top', 'top_right', 'right', 'bottom_right', 'bottom', 'bottom_left', 'center', 'rear_side', 'edge', 'other',
diff --git a/src/MDObjectPublicationBackgrounds.php b/src/MDObjectPublicationBackgrounds.php
index 015034c..1d68d4b 100644
--- a/src/MDObjectPublicationBackgrounds.php
+++ b/src/MDObjectPublicationBackgrounds.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available marking types.
  */
-class MDObjectPublicationBackgrounds extends MDValueSet {
+final class MDObjectPublicationBackgrounds extends MDValueSet {
 
     const PUBLICATION_BACKGROUNDS = [
         '0', // Image published
diff --git a/src/MDPlacetypesSet.php b/src/MDPlacetypesSet.php
index a59df53..4cfcb33 100644
--- a/src/MDPlacetypesSet.php
+++ b/src/MDPlacetypesSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available place types.
  */
-class MDPlacetypesSet extends MDValueSet {
+final class MDPlacetypesSet extends MDValueSet {
 
     const PLACE_TYPE_IDS = [
         '0', // => Administrativ
diff --git a/src/MDTitleTypesSet.php b/src/MDTitleTypesSet.php
index c890b84..6156bc5 100644
--- a/src/MDTitleTypesSet.php
+++ b/src/MDTitleTypesSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available marking types.
  */
-class MDTitleTypesSet extends MDValueSet {
+final class MDTitleTypesSet extends MDValueSet {
 
     const TITLE_TYPES = [
         "",
diff --git a/src/MDUnitsSet.php b/src/MDUnitsSet.php
index a467097..f07d263 100644
--- a/src/MDUnitsSet.php
+++ b/src/MDUnitsSet.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class containing available units for weights, lengths etc.
  */
-class MDUnitsSet extends MDValueSet {
+final class MDUnitsSet extends MDValueSet {
 
     const UNITS_LENGTH = ['', 'm', 'dm', 'cm', 'mm'];
     const UNITS_WEIGHT = ['', 't', 'kg', 'g'];