diff --git a/subprojects/groovy-jsr223/src/main/java/org/codehaus/groovy/jsr223/GroovyScriptEngineImpl.java b/subprojects/groovy-jsr223/src/main/java/org/codehaus/groovy/jsr223/GroovyScriptEngineImpl.java
index 82a8507..4692a92 100644
--- a/subprojects/groovy-jsr223/src/main/java/org/codehaus/groovy/jsr223/GroovyScriptEngineImpl.java
+++ b/subprojects/groovy-jsr223/src/main/java/org/codehaus/groovy/jsr223/GroovyScriptEngineImpl.java
@@ -75,9 +75,9 @@ import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
 
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 /*
  * @author Mike Grogan
@@ -108,8 +108,8 @@ public class GroovyScriptEngineImpl
     }
 
     public GroovyScriptEngineImpl() {
-        classMap = Collections.synchronizedMap(new HashMap<String, Class>());
-        globalClosures = Collections.synchronizedMap(new HashMap<String, Closure>());
+        classMap = new ConcurrentHashMap<String, Class>();
+        globalClosures = new ConcurrentHashMap<String, Closure>();
         loader = new GroovyClassLoader(getParentLoader(),
                 new CompilerConfiguration());
     }