diff --git a/UPGRADE.md b/UPGRADE.md
index ea2c03324b9..a4412a6c83c 100644
--- a/UPGRADE.md
+++ b/UPGRADE.md
@@ -12,6 +12,7 @@ The Doctrine\DBAL\Version class is no longer available: please refrain from chec
 ## BC BREAK: the SQLLogger interface has changed
 
 The methods are the same but use scalar type hints, return types, and non-nullable arrays.
+SQLLogger implementations are now final.
 
 Before:
 
diff --git a/lib/Doctrine/DBAL/Logging/DebugStack.php b/lib/Doctrine/DBAL/Logging/DebugStack.php
index 5d2c8cf62ab..bd1358f321d 100644
--- a/lib/Doctrine/DBAL/Logging/DebugStack.php
+++ b/lib/Doctrine/DBAL/Logging/DebugStack.php
@@ -7,7 +7,7 @@
 /**
  * Includes executed SQLs in a Debug Stack.
  */
-class DebugStack implements SQLLogger
+final class DebugStack implements SQLLogger
 {
     /**
      * Executed SQL queries.
diff --git a/lib/Doctrine/DBAL/Logging/EchoSQLLogger.php b/lib/Doctrine/DBAL/Logging/EchoSQLLogger.php
index 4a7da004cb7..cfca9dd7c90 100644
--- a/lib/Doctrine/DBAL/Logging/EchoSQLLogger.php
+++ b/lib/Doctrine/DBAL/Logging/EchoSQLLogger.php
@@ -8,7 +8,7 @@
 /**
  * A SQL logger that logs to the standard output using echo/var_dump.
  */
-class EchoSQLLogger implements SQLLogger
+final class EchoSQLLogger implements SQLLogger
 {
     /**
      * {@inheritdoc}
diff --git a/lib/Doctrine/DBAL/Logging/LoggerChain.php b/lib/Doctrine/DBAL/Logging/LoggerChain.php
index 2eaac3e02e4..598f51e2a6b 100644
--- a/lib/Doctrine/DBAL/Logging/LoggerChain.php
+++ b/lib/Doctrine/DBAL/Logging/LoggerChain.php
@@ -5,7 +5,7 @@
 /**
  * Chains multiple SQLLogger.
  */
-class LoggerChain implements SQLLogger
+final class LoggerChain implements SQLLogger
 {
     /** @var SQLLogger[] */
     private $loggers = [];