diff --git a/java/src/main/java/org/msgpack/BufferedUnpackerImpl.java b/java/src/main/java/org/msgpack/BufferedUnpackerImpl.java
index 9496238f..5b449c79 100644
--- a/java/src/main/java/org/msgpack/BufferedUnpackerImpl.java
+++ b/java/src/main/java/org/msgpack/BufferedUnpackerImpl.java
@@ -19,7 +19,7 @@ package org.msgpack;
 
 import java.io.IOException;
 import java.nio.ByteBuffer;
-//import java.math.BigInteger;
+import java.math.BigInteger;
 
 abstract class BufferedUnpackerImpl extends UnpackerImpl {
 	int offset = 0;
@@ -198,8 +198,7 @@ abstract class BufferedUnpackerImpl extends UnpackerImpl {
 			{
 				long o = castBuffer.getLong(0);
 				if(o < 0) {
-					// FIXME unpackBigInteger
-					throw new MessageTypeException("uint 64 bigger than 0x7fffffff is not supported");
+					throw new MessageTypeException();
 				}
 				advance(9);
 				return o;
@@ -231,7 +230,25 @@ abstract class BufferedUnpackerImpl extends UnpackerImpl {
 		}
 	}
 
-	// FIXME unpackBigInteger
+	final BigInteger unpackBigInteger() throws IOException, MessageTypeException {
+		more(1);
+		int b = buffer[offset];
+		if((b & 0xff) != 0xcf) {
+			return BigInteger.valueOf(unpackLong());
+		}
+
+		// unsigned int 64
+		more(9);
+		castBuffer.rewind();
+		castBuffer.put(buffer, offset+1, 8);
+		advance(9);
+		long o = castBuffer.getLong(0);
+		if(o < 0) {
+			return new BigInteger(1, castBuffer.array());
+		} else {
+			return BigInteger.valueOf(o);
+		}
+	}
 
 	final float unpackFloat() throws IOException, MessageTypeException {
 		more(1);
diff --git a/java/src/main/java/org/msgpack/Unpacker.java b/java/src/main/java/org/msgpack/Unpacker.java
index 3a952438..3cae502e 100644
--- a/java/src/main/java/org/msgpack/Unpacker.java
+++ b/java/src/main/java/org/msgpack/Unpacker.java
@@ -22,6 +22,7 @@ import java.io.InputStream;
 import java.io.IOException;
 import java.util.Iterator;
 import java.nio.ByteBuffer;
+import java.math.BigInteger;
 
 /**
  * Unpacker enables you to deserialize objects from stream.
@@ -452,6 +453,15 @@ public class Unpacker implements Iterable<MessagePackObject> {
 		return impl.unpackLong();
 	}
 
+	/**
+	 * Gets one {@code BigInteger} value from the buffer.
+	 * This method calls {@link fill()} method if needed.
+	 * @throws MessageTypeException the first value of the buffer is not a {@code BigInteger}.
+	 */
+	public BigInteger unpackBigInteger() throws IOException, MessageTypeException {
+		return impl.unpackBigInteger();
+	}
+
 	/**
 	 * Gets one {@code float} value from the buffer.
 	 * This method calls {@link fill()} method if needed.
diff --git a/java/src/test/java/org/msgpack/TestDirectConversion.java b/java/src/test/java/org/msgpack/TestDirectConversion.java
index dbacf012..1822ecb4 100644
--- a/java/src/test/java/org/msgpack/TestDirectConversion.java
+++ b/java/src/test/java/org/msgpack/TestDirectConversion.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.*;
@@ -48,6 +49,29 @@ public class TestDirectConversion {
 		assertEquals(val, pac.unpackLong());
 	}
 
+	@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 testBigInteger(BigInteger val) throws Exception {
+		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		new Packer(out).pack(val);
+		ByteArrayInputStream in = new ByteArrayInputStream(out.toByteArray());
+		Unpacker pac = new Unpacker(in);
+		assertEquals(val, pac.unpackBigInteger());
+	}
+
 	@Test
 	public void testFloat() throws Exception {
 		testFloat((float)0.0);