diff --git a/querydsl-core/src/main/java/com/mysema/query/JoinExpression.java b/querydsl-core/src/main/java/com/mysema/query/JoinExpression.java
index 375284dca..1928a55d6 100644
--- a/querydsl-core/src/main/java/com/mysema/query/JoinExpression.java
+++ b/querydsl-core/src/main/java/com/mysema/query/JoinExpression.java
@@ -24,7 +24,7 @@ public final class JoinExpression implements Serializable{
 
     private static final long serialVersionUID = -1131755765747174886L;
 
-    private BooleanBuilder condition = new BooleanBuilder();
+    private final BooleanBuilder condition = new BooleanBuilder();
 
     private final Set<JoinFlag> flags = new LinkedHashSet<JoinFlag>();