diff --git a/src/core/lombok/core/AST.java b/src/core/lombok/core/AST.java
index e6efe058..2d5e5352 100644
--- a/src/core/lombok/core/AST.java
+++ b/src/core/lombok/core/AST.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2009-2013 The Project Lombok Authors.
+ * Copyright (C) 2009-2016 The Project Lombok Authors.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -21,7 +21,7 @@
  */
 package lombok.core;
 
-import static lombok.Lombok.*;
+import static lombok.Lombok.sneakyThrow;
 
 import java.lang.reflect.Array;
 import java.lang.reflect.Field;
@@ -31,10 +31,11 @@ import java.lang.reflect.Type;
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.HashMap;
 import java.util.IdentityHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 import lombok.core.configuration.ConfigurationKey;
 import lombok.core.debug.HistogramTracker;
@@ -209,11 +210,11 @@ public abstract class AST<A extends AST<A, L, N>, L extends LombokNode<A, L, N>,
 		}
 	}
 	
-	private static Map<Class<?>, Collection<FieldAccess>> fieldsOfASTClasses = new HashMap<Class<?>, Collection<FieldAccess>>();
+	private static final ConcurrentMap<Class<?>, Collection<FieldAccess>> fieldsOfASTClasses = new ConcurrentHashMap<Class<?>, Collection<FieldAccess>>();
 	
 	/** Returns FieldAccess objects for the stated class. Each field that contains objects of the kind returned by
 	 * {@link #getStatementTypes()}, either directly or inside of an array or java.util.collection (or array-of-arrays,
-	 * or collection-of-collections, etcetera), is returned.
+	 * or collection-of-collections, et cetera), is returned.
 	 */
 	protected Collection<FieldAccess> fieldsOf(Class<?> c) {
 		Collection<FieldAccess> fields = fieldsOfASTClasses.get(c);
@@ -221,8 +222,8 @@ public abstract class AST<A extends AST<A, L, N>, L extends LombokNode<A, L, N>,
 		
 		fields = new ArrayList<FieldAccess>();
 		getFields(c, fields);
-		fieldsOfASTClasses.put(c, fields);
-		return fields;
+		fieldsOfASTClasses.putIfAbsent(c, fields);
+		return fieldsOfASTClasses.get(c);
 	}
 	
 	private void getFields(Class<?> c, Collection<FieldAccess> fields) {