diff --git a/java/src/main/java/org/msgpack/MessageConvertable.java b/java/src/main/java/org/msgpack/MessageConvertable.java
index da251dc1..8acf1f28 100644
--- a/java/src/main/java/org/msgpack/MessageConvertable.java
+++ b/java/src/main/java/org/msgpack/MessageConvertable.java
@@ -18,6 +18,6 @@
 package org.msgpack;
 
 public interface MessageConvertable {
-	public void messageConvert(Object obj) throws MessageTypeException;
+	public void messageConvert(MessagePackObject obj) throws MessageTypeException;
 }
 
diff --git a/java/src/main/java/org/msgpack/Packer.java b/java/src/main/java/org/msgpack/Packer.java
index 98af3d64..60e04bfe 100644
--- a/java/src/main/java/org/msgpack/Packer.java
+++ b/java/src/main/java/org/msgpack/Packer.java
@@ -196,19 +196,19 @@ public class Packer {
 	}
 
 	public Packer packBigInteger(BigInteger d) throws IOException {
-		if(d.compareTo(BigInteger.valueOf(Long.MAX_VALUE)) <= 0) {
+		if(d.bitLength() <= 63) {
 			return packLong(d.longValue());
-		} else if(d.bitLength() <= 64) {
+		} else if(d.bitLength() <= 64 && d.signum() >= 0) {
 			castBytes[0] = (byte)0xcf;
 			byte[] barray = d.toByteArray();
-			castBytes[1] = barray[0];
-			castBytes[2] = barray[1];
-			castBytes[3] = barray[2];
-			castBytes[4] = barray[3];
-			castBytes[5] = barray[4];
-			castBytes[6] = barray[5];
-			castBytes[7] = barray[6];
-			castBytes[8] = barray[7];
+			castBytes[1] = barray[barray.length-8];
+			castBytes[2] = barray[barray.length-7];
+			castBytes[3] = barray[barray.length-6];
+			castBytes[4] = barray[barray.length-5];
+			castBytes[5] = barray[barray.length-4];
+			castBytes[6] = barray[barray.length-3];
+			castBytes[7] = barray[barray.length-2];
+			castBytes[8] = barray[barray.length-1];
 			out.write(castBytes);
 			return this;
 		} else {
@@ -436,6 +436,8 @@ public class Packer {
 			return packFloat((Float)o);
 		} else if(o instanceof Double) {
 			return packDouble((Double)o);
+		} else if(o instanceof BigInteger) {
+			return packBigInteger((BigInteger)o);
 		} else {
 			throw new MessageTypeException("unknown object "+o+" ("+o.getClass()+")");
 		}
diff --git a/java/src/main/java/org/msgpack/UnpackerImpl.java b/java/src/main/java/org/msgpack/UnpackerImpl.java
index d4f99e38..6a7085fb 100644
--- a/java/src/main/java/org/msgpack/UnpackerImpl.java
+++ b/java/src/main/java/org/msgpack/UnpackerImpl.java
@@ -18,6 +18,7 @@
 package org.msgpack;
 
 import java.nio.ByteBuffer;
+import java.math.BigInteger;
 import org.msgpack.object.*;
 
 public class UnpackerImpl {
@@ -262,9 +263,7 @@ public class UnpackerImpl {
 						{
 							long o = castBuffer.getLong(0);
 							if(o < 0) {
-								// FIXME
-								//obj = GenericBigInteger.valueOf(o & 0x7fffffffL).setBit(31);
-								throw new UnpackException("uint 64 bigger than 0x7fffffff is not supported");
+								obj = IntegerType.create(new BigInteger(1, castBuffer.array()));
 							} else {
 								obj = IntegerType.create(o);
 							}
diff --git a/java/src/test/java/org/msgpack/TestPackUnpack.java b/java/src/test/java/org/msgpack/TestPackUnpack.java
index ca3d235c..75c5fe74 100644
--- a/java/src/test/java/org/msgpack/TestPackUnpack.java
+++ b/java/src/test/java/org/msgpack/TestPackUnpack.java
@@ -3,6 +3,7 @@ package org.msgpack;
 import org.msgpack.*;
 import java.io.*;
 import java.util.*;
+import java.math.BigInteger;
 
 import org.junit.Test;
 import static org.junit.Assert.*;
@@ -36,6 +37,32 @@ public class TestPackUnpack {
 			testInt(rand.nextInt());
 	}
 
+	public void testBigInteger(BigInteger val) throws Exception {
+		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		new Packer(out).pack(val);
+		MessagePackObject obj = unpackOne(out);
+		if(!val.equals(obj.asBigInteger())) {
+			System.out.println("expect: "+val);
+			System.out.println("but   : "+obj.asBigInteger());
+		}
+		assertEquals(val, obj.asBigInteger());
+	}
+	@Test
+	public void testBigInteger() throws Exception {
+		testBigInteger(BigInteger.valueOf(0));
+		testBigInteger(BigInteger.valueOf(-1));
+		testBigInteger(BigInteger.valueOf(1));
+		testBigInteger(BigInteger.valueOf(Integer.MIN_VALUE));
+		testBigInteger(BigInteger.valueOf(Integer.MAX_VALUE));
+		testBigInteger(BigInteger.valueOf(Long.MIN_VALUE));
+		testBigInteger(BigInteger.valueOf(Long.MAX_VALUE));
+		BigInteger max = BigInteger.valueOf(Long.MAX_VALUE).setBit(63);
+		testBigInteger(max);
+		Random rand = new Random();
+		for (int i = 0; i < 1000; i++)
+			testBigInteger( max.subtract(BigInteger.valueOf( Math.abs(rand.nextLong()) )) );
+	}
+
 	public void testFloat(float val) throws Exception {
 		ByteArrayOutputStream out = new ByteArrayOutputStream();
 		new Packer(out).pack(val);