diff --git a/plugins/org.eclipse.dltk.javascript.core/src/org/eclipse/dltk/internal/javascript/ti/ElementValue.java b/plugins/org.eclipse.dltk.javascript.core/src/org/eclipse/dltk/internal/javascript/ti/ElementValue.java
index d0d6c3c..f2438ea 100644
--- a/plugins/org.eclipse.dltk.javascript.core/src/org/eclipse/dltk/internal/javascript/ti/ElementValue.java
+++ b/plugins/org.eclipse.dltk.javascript.core/src/org/eclipse/dltk/internal/javascript/ti/ElementValue.java
@@ -18,6 +18,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.eclipse.dltk.annotations.Internal;
 import org.eclipse.dltk.compiler.problem.IProblemIdentifier;
@@ -356,7 +357,7 @@
 
 	static class TypeValue extends ElementValue implements IValue {
 
-		private final Map<String, IValue> children = new HashMap<String, IValue>(
+		private final Map<String, IValue> children = new ConcurrentHashMap<String, IValue>(
 				4, 0.9f);
 
 		private final JSTypeSet types;
diff --git a/plugins/org.eclipse.dltk.javascript.core/src/org/eclipse/dltk/internal/javascript/ti/ImmutableValue.java b/plugins/org.eclipse.dltk.javascript.core/src/org/eclipse/dltk/internal/javascript/ti/ImmutableValue.java
index b62ef97..dce162e 100644
--- a/plugins/org.eclipse.dltk.javascript.core/src/org/eclipse/dltk/internal/javascript/ti/ImmutableValue.java
+++ b/plugins/org.eclipse.dltk.javascript.core/src/org/eclipse/dltk/internal/javascript/ti/ImmutableValue.java
@@ -6,6 +6,7 @@
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.eclipse.dltk.javascript.typeinference.ReferenceKind;
 import org.eclipse.dltk.javascript.typeinference.ReferenceLocation;
@@ -290,16 +291,19 @@
 				value = ElementValue.findMemberA(declaredType, name, resolve);
 				if (value != null) {
 					if (elementValues == null)
-						elementValues = new HashMap<String, IValue>(4, 0.9f);
+						elementValues = new ConcurrentHashMap<String, IValue>(
+								4, 0.9f);
 					elementValues.put(name, value);
 					return value;
+
 				}
 			}
 			for (IRType type : types) {
 				value = ElementValue.findMemberA(type, name, resolve);
 				if (value != null) {
 					if (elementValues == null)
-						elementValues = new HashMap<String, IValue>(4, 0.9f);
+						elementValues = new ConcurrentHashMap<String, IValue>(
+								4, 0.9f);
 					if (resolve && value instanceof ElementValue) {
 						value = ((ElementValue) value).resolveValue();
 					}