diff --git a/tests/Functional/PortabilityTest.php b/tests/Functional/PortabilityTest.php
index 9a11859f5b6..3fef5445a11 100644
--- a/tests/Functional/PortabilityTest.php
+++ b/tests/Functional/PortabilityTest.php
@@ -49,7 +49,9 @@ protected function setUp(): void
 
     protected function tearDown(): void
     {
-        $this->markConnectionNotReusable();
+        // the connection that overrides the shared one has to be manually closed prior to 4.0.0 to prevent leak
+        // see https://github.com/doctrine/dbal/issues/4515
+        $this->connection->close();
     }
 
     public function testFullFetchMode(): void
diff --git a/tests/Functional/Schema/MySQLSchemaManagerTest.php b/tests/Functional/Schema/MySQLSchemaManagerTest.php
index 5a960a23378..5f0d722bc65 100644
--- a/tests/Functional/Schema/MySQLSchemaManagerTest.php
+++ b/tests/Functional/Schema/MySQLSchemaManagerTest.php
@@ -21,11 +21,6 @@ public static function setUpBeforeClass(): void
         Type::addType('point', PointType::class);
     }
 
-    protected function tearDown(): void
-    {
-        $this->markConnectionNotReusable();
-    }
-
     protected function supportsPlatform(AbstractPlatform $platform): bool
     {
         return $platform instanceof MySQLPlatform;
@@ -106,6 +101,9 @@ public function testSpatialIndex(): void
 
         $this->schemaManager->dropAndCreateTable($table);
 
+        // see https://github.com/doctrine/dbal/issues/4983
+        $this->markConnectionNotReusable();
+
         $indexes = $this->schemaManager->listTableIndexes('spatial_index');
         self::assertArrayHasKey('s_index', $indexes);
         self::assertTrue($indexes['s_index']->hasFlag('spatial'));
diff --git a/tests/Functional/Schema/PostgreSQLSchemaManagerTest.php b/tests/Functional/Schema/PostgreSQLSchemaManagerTest.php
index 831af69c0ac..c9ce4aeb3ab 100644
--- a/tests/Functional/Schema/PostgreSQLSchemaManagerTest.php
+++ b/tests/Functional/Schema/PostgreSQLSchemaManagerTest.php
@@ -198,6 +198,8 @@ public function testFilterSchemaExpression(): void
         $testTable->addColumn('id', 'integer');
         $this->schemaManager->createTable($testTable);
 
+        $this->markConnectionNotReusable();
+
         $this->connection->getConfiguration()->setSchemaAssetsFilter(static function (string $name): bool {
             return preg_match('#^dbal204_#', $name) === 1;
         });
diff --git a/tests/Functional/Schema/SchemaManagerFunctionalTestCase.php b/tests/Functional/Schema/SchemaManagerFunctionalTestCase.php
index e578e06ba3c..d5a809abc50 100644
--- a/tests/Functional/Schema/SchemaManagerFunctionalTestCase.php
+++ b/tests/Functional/Schema/SchemaManagerFunctionalTestCase.php
@@ -78,8 +78,6 @@ protected function tearDown(): void
             $this->connection->executeStatement('DROP SCHEMA testschema');
         } catch (Exception $e) {
         }
-
-        $this->markConnectionNotReusable();
     }
 
     public function testDropAndCreateSequence(): void