diff --git a/spring-session-core/src/main/java/org/springframework/session/web/http/HttpSessionAdapter.java b/spring-session-core/src/main/java/org/springframework/session/web/http/HttpSessionAdapter.java
index 1a6e4f90..9dd35a2d 100644
--- a/spring-session-core/src/main/java/org/springframework/session/web/http/HttpSessionAdapter.java
+++ b/spring-session-core/src/main/java/org/springframework/session/web/http/HttpSessionAdapter.java
@@ -42,7 +42,7 @@ class HttpSessionAdapter<S extends Session> implements HttpSession {
 
 	private static final Log logger = LogFactory.getLog(HttpSessionAdapter.class);
 
-	private S session;
+	private final S session;
 
 	private final ServletContext servletContext;