diff --git a/lib/java/src/org/apache/thrift/meta_data/FieldMetaData.java b/lib/java/src/org/apache/thrift/meta_data/FieldMetaData.java
index 445f7e4..7534390 100644
--- a/lib/java/src/org/apache/thrift/meta_data/FieldMetaData.java
+++ b/lib/java/src/org/apache/thrift/meta_data/FieldMetaData.java
@@ -21,6 +21,8 @@
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
 import org.apache.thrift.TBase;
 import org.apache.thrift.TFieldIdEnum;
 
@@ -28,15 +30,22 @@
  * This class is used to store meta data about thrift fields. Every field in a
  * a struct should have a corresponding instance of this class describing it.
  *
+ * The meta data is registered by ALL Thrift struct classes via a static {...}
+ * initializer block in the generated Thrift code.
+ *
+ * Since different threads could be initializing different Thrift classes, calls
+ * to the public static methods of this class could be racy.
+ *
+ * All methods of this class should be made thread safe.
  */
 public class FieldMetaData implements java.io.Serializable {
   public final String fieldName;
   public final byte requirementType;
   public final FieldValueMetaData valueMetaData;
-  private static Map<Class<? extends TBase>, Map<? extends TFieldIdEnum, FieldMetaData>> structMap;
+  private static final Map<Class<? extends TBase>, Map<? extends TFieldIdEnum, FieldMetaData>> structMap;
   
   static {
-    structMap = new HashMap<Class<? extends TBase>, Map<? extends TFieldIdEnum, FieldMetaData>>();
+    structMap = new ConcurrentHashMap<Class<? extends TBase>, Map<? extends TFieldIdEnum, FieldMetaData>>();
   }
   
   public FieldMetaData(String name, byte req, FieldValueMetaData vMetaData){
@@ -45,7 +54,7 @@
     this.valueMetaData = vMetaData;
   }
   
-  public static synchronized void addStructMetaDataMap(Class<? extends TBase> sClass, Map<? extends TFieldIdEnum, FieldMetaData> map){
+  public static void addStructMetaDataMap(Class<? extends TBase> sClass, Map<? extends TFieldIdEnum, FieldMetaData> map){
     structMap.put(sClass, map);
   }
 
@@ -53,9 +62,18 @@
    * Returns a map with metadata (i.e. instances of FieldMetaData) that
    * describe the fields of the given class.
    *
-   * @param sClass The TBase class for which the metadata map is requested
+   * @param sClass The TBase class for which the metadata map is requested. It is not
+   *               guaranteed that sClass will have been statically initialized before
+   *               this method is called. A racy call to
+   *               {@link FieldMetaData#addStructMetaDataMap(Class, Map)} from a different
+   *               thread during static initialization of the Thrift class is possible.
    */
-  public static synchronized Map<? extends TFieldIdEnum, FieldMetaData> getStructMetaDataMap(Class<? extends TBase> sClass){
+  public static Map<? extends TFieldIdEnum, FieldMetaData> getStructMetaDataMap(
+      Class<? extends TBase> sClass) {
+    // Note: Do not use synchronized on this method declaration - it leads to a deadlock.
+    // Similarly, do not trigger sClass.newInstance() while holding a lock on structMap,
+    // it will lead to the same deadlock.
+    // See: https://issues.apache.org/jira/browse/THRIFT-5430 for details.
     if (!structMap.containsKey(sClass)){ // Load class if it hasn't been loaded
       try{
         sClass.newInstance();
diff --git a/lib/javame/src/org/apache/thrift/meta_data/FieldMetaData.java b/lib/javame/src/org/apache/thrift/meta_data/FieldMetaData.java
index bce02c7..333f4ee 100644
--- a/lib/javame/src/org/apache/thrift/meta_data/FieldMetaData.java
+++ b/lib/javame/src/org/apache/thrift/meta_data/FieldMetaData.java
@@ -46,12 +46,19 @@
  * This class is used to store meta data about thrift fields. Every field in a
  * a struct should have a corresponding instance of this class describing it.
  *
+ * The meta data is registered by ALL Thrift struct classes via a static {...}
+ * initializer block in the generated Thrift code.
+ *
+ * Since different threads could be initializing different Thrift classes, calls
+ * to the public static methods of this class could be racy.
+ *
+ * All methods of this class should be made thread safe.
  */
 public class FieldMetaData  {
   public final String fieldName;
   public final byte requirementType;
   public final FieldValueMetaData valueMetaData;
-  private static Hashtable structMap;
+  private static final Hashtable structMap;
   
   static {
     structMap = new Hashtable();
@@ -63,18 +70,33 @@
     this.valueMetaData = vMetaData;
   }
   
-  public static synchronized void addStructMetaDataMap(Class sClass, Hashtable map){
-    structMap.put(sClass, map);
+  public static void addStructMetaDataMap(Class sClass, Hashtable map){
+    synchronized (structMap) {
+      structMap.put(sClass, map);
+    }
   }
 
   /**
    * Returns a map with metadata (i.e. instances of FieldMetaData) that
    * describe the fields of the given class.
    *
-   * @param sClass The TBase class for which the metadata map is requested
+   * @param sClass The TBase class for which the metadata map is requested. It is not
+   *               guaranteed that sClass will have been statically initialized before
+   *               this method is called. A racy call to
+   *               {@link FieldMetaData#addStructMetaDataMap(Class, Hashtable)} from a different
+   *               thread during static initialization of the Thrift class is possible.
    */
-  public static synchronized Hashtable getStructMetaDataMap(Class sClass){
-    if (!structMap.containsKey(sClass)){ // Load class if it hasn't been loaded
+  public static Hashtable getStructMetaDataMap(Class sClass) {
+    // Note: Do not use synchronized on this method declaration - it leads to a deadlock.
+    // Similarly, do not trigger sClass.newInstance() while holding a lock on structMap,
+    // it will lead to the same deadlock.
+    // See: https://issues.apache.org/jira/browse/THRIFT-5430 for details.
+    boolean isThriftStructStaticallyInitialized = false;
+    synchronized (structMap) {
+      isThriftStructStaticallyInitialized = structMap.containsKey(sClass);
+    }
+
+    if (!isThriftStructStaticallyInitialized){ // Load class if it hasn't been loaded
       try{
         sClass.newInstance();
       } catch (InstantiationException e){
@@ -83,6 +105,8 @@
         throw new RuntimeException("IllegalAccessException for TBase class: " + sClass.getName() + ", message: " + e.getMessage());
       }
     }
-    return (Hashtable) structMap.get(sClass);
+    synchronized (structMap) {
+      return (Hashtable) structMap.get(sClass);
+    }
   }
 }