diff --git a/exceptions/MDConsoleInvalidHeadingNumber.php b/exceptions/MDConsoleInvalidHeadingNumber.php
index d527c3e..e81d9aa 100644
--- a/exceptions/MDConsoleInvalidHeadingNumber.php
+++ b/exceptions/MDConsoleInvalidHeadingNumber.php
@@ -4,7 +4,7 @@ declare(strict_types = 1);
 /**
  * Custom exception class for invalid page parameters.
  */
-class MDConsoleInvalidHeadingNumber extends Exception {
+final class MDConsoleInvalidHeadingNumber extends Exception {
 
     /**
      * Error message.
diff --git a/src/MDConsole.php b/src/MDConsole.php
index 87e71da..f6ff8fa 100644
--- a/src/MDConsole.php
+++ b/src/MDConsole.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Interface for CLI outputs of museum-digital's dev and admin tools.
  */
-class MDConsole {
+final class MDConsole {
 
     const STATUS_NOTICE = 0;
     const STATUS_UPDATE = 1;
diff --git a/src/MDOutputHandler.php b/src/MDOutputHandler.php
index adf1e8f..899489a 100644
--- a/src/MDOutputHandler.php
+++ b/src/MDOutputHandler.php
@@ -9,7 +9,7 @@ declare(strict_types = 1);
 /**
  * Class for handling outputs and logs for museum-digital's background tools.
  */
-class MDOutputHandler {
+final class MDOutputHandler {
 
     /*
      * Variables