diff --git a/src/main/java/de/dhbwstuttgart/typeinference/unify/TypeUnifyTask.java b/src/main/java/de/dhbwstuttgart/typeinference/unify/TypeUnifyTask.java
index 54b07cb..b9d071a 100644
--- a/src/main/java/de/dhbwstuttgart/typeinference/unify/TypeUnifyTask.java
+++ b/src/main/java/de/dhbwstuttgart/typeinference/unify/TypeUnifyTask.java
@@ -130,7 +130,7 @@ public class TypeUnifyTask extends RecursiveTask<Set<Set<UnifyPair>>>  {
 	volatile UnifyTaskModel usedTasks;
 	
 	static Writer statistics;
-	protected ConstraintSetRepository constraintSetRepository;
+	protected volatile ConstraintSetRepository constraintSetRepository;
 	
 	public TypeUnifyTask() { 
 		rules = new RuleSet();