diff --git a/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/PdoSessionHandler.php b/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/PdoSessionHandler.php
index cdae297d93..0fd34dc1b6 100644
--- a/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/PdoSessionHandler.php
+++ b/src/Symfony/Component/HttpFoundation/Session/Storage/Handler/PdoSessionHandler.php
@@ -637,7 +637,9 @@ class PdoSessionHandler extends AbstractSessionHandler
                 throw new \RuntimeException('Failed to read session: INSERT reported a duplicate id but next SELECT did not return any data.');
             }
 
-            if (self::LOCK_TRANSACTIONAL === $this->lockMode && 'sqlite' !== $this->driver) {
+            if (!ini_get('session.use_strict_mode') && self::LOCK_TRANSACTIONAL === $this->lockMode && 'sqlite' !== $this->driver) {
+                // In strict mode, session fixation is not possible: new sessions always start with a unique
+                // random id, so that concurrency is not possible and this code path can be skipped.
                 // Exclusive-reading of non-existent rows does not block, so we need to do an insert to block
                 // until other connections to the session are committed.
                 try {