Index: common/src/java/org/apache/ldap/common/schema/CachingNormalizer.java
===================================================================
--- common/src/java/org/apache/ldap/common/schema/CachingNormalizer.java	(revision 280676)
+++ common/src/java/org/apache/ldap/common/schema/CachingNormalizer.java	(working copy)
@@ -75,13 +75,29 @@
      */
     public Object normalize( Object value ) throws NamingException
     {
-        if ( cache.containsKey( value ) )
+        Object normalized;
+        
+        /*
+         * Use of R/W lock is more appropriate here. Consider using JSR 166
+         * backport ConcurrentHashMap or ReentrantReadWriteLock. Get read lock
+         * for this block.
+         */ 
+        synchronized ( cache )
         {
-            return cache.get( value ) ;
+            normalized = cache.get( value ) ;
+            if (null != normalized || cache.containsKey( value ))
+            {
+                return normalized;
+            }
         }
+
+        normalized = normalizer.normalize( value ) ;
+        // Get write lock for this block.
+        synchronized ( cache )
+        {
+            cache.put( value, normalized ) ;
+        }
         
-        Object normalized = normalizer.normalize( value ) ;
-        cache.put( value, normalized ) ;
         return normalized ;
     }
 }