diff --git a/src/Symfony/Component/HttpFoundation/Session/Session.php b/src/Symfony/Component/HttpFoundation/Session/Session.php
index 62ce948b6828..867ceba97f8d 100644
--- a/src/Symfony/Component/HttpFoundation/Session/Session.php
+++ b/src/Symfony/Component/HttpFoundation/Session/Session.php
@@ -193,9 +193,7 @@ public function migrate($destroy = false, $lifetime = null)
      */
     public function save()
     {
-        if ($this->isStarted()) {
-            $this->storage->save();
-        }
+        $this->storage->save();
     }
 
     /**
diff --git a/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php b/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php
index c4dbe7586822..13d0a2034d5f 100644
--- a/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php
+++ b/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php
@@ -219,6 +219,11 @@ public function regenerate($destroy = false, $lifetime = null)
      */
     public function save()
     {
+        // In PHP <7.2 session_write_close() returns void if the session is not started.
+        // @see https://www.php.net/manual/function.session-write-close.php
+        if (!$this->started) {
+            return;
+        }
         $session = $_SESSION;
 
         foreach ($this->bags as $bag) {
diff --git a/src/Symfony/Component/HttpFoundation/Tests/Session/SessionTest.php b/src/Symfony/Component/HttpFoundation/Tests/Session/SessionTest.php
index e75b3321b035..afa00fc7c304 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/Session/SessionTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/Session/SessionTest.php
@@ -260,14 +260,4 @@ public function testIsEmpty()
         $flash->get('hello');
         $this->assertTrue($this->session->isEmpty());
     }
-
-    public function testSaveIfNotStarted()
-    {
-        $storage = $this->getMockBuilder('Symfony\Component\HttpFoundation\Session\Storage\SessionStorageInterface')->getMock();
-        $session = new Session($storage);
-
-        $storage->expects($this->once())->method('isStarted')->willReturn(false);
-        $storage->expects($this->never())->method('save');
-        $session->save();
-    }
 }
diff --git a/src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php b/src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php
index 7cc2eb79c8db..25a2d8c9c17a 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php
@@ -105,6 +105,13 @@ public function testGetId()
         $this->assertSame($id, $storage->getId(), 'ID stays after saving session');
     }
 
+    public function testSaveIfNotStarted()
+    {
+        $storage = $this->getStorage();
+        $this->assertNull($storage->save(), 'Saving unstarted sessions does not error');
+        $this->assertEmpty(glob($this->savePath.'/*'));
+    }
+
     public function testRegenerate()
     {
         $storage = $this->getStorage();