diff --git a/src/BtBitfieldMessage.cc b/src/BtBitfieldMessage.cc
index 6992d281..6ba1d97e 100644
--- a/src/BtBitfieldMessage.cc
+++ b/src/BtBitfieldMessage.cc
@@ -104,8 +104,8 @@ unsigned char* BtBitfieldMessage::createMessage() {
   /**
    * len --- 1+bitfieldLength, 4bytes
    * id --- 5, 1byte
-   * bitfield --- bitfield, len bytes
-   * total: 5+len bytes
+   * bitfield --- bitfield, bitfieldLength bytes
+   * total: 5+bitfieldLength bytes
    */
   const size_t msgLength = 5+bitfieldLength_;
   unsigned char* msg = new unsigned char[msgLength];
diff --git a/src/PeerConnection.cc b/src/PeerConnection.cc
index 2af5383b..da715929 100644
--- a/src/PeerConnection.cc
+++ b/src/PeerConnection.cc
@@ -57,7 +57,8 @@ PeerConnection::PeerConnection
   : cuid_(cuid),
     peer_(peer),
     socket_(socket),
-    resbuf_(new unsigned char[MAX_PAYLOAD_LEN]),
+    maxPayloadLength_(MAX_PAYLOAD_LEN),
+    resbuf_(new unsigned char[maxPayloadLength_]),
     resbufLength_(0),
     currentPayloadLength_(0),
     lenbufLength_(0),
@@ -105,7 +106,7 @@ bool PeerConnection::receiveMessage(unsigned char* data, size_t& dataLength) {
     uint32_t payloadLength;
     memcpy(&payloadLength, lenbuf_, sizeof(payloadLength));
     payloadLength = ntohl(payloadLength);
-    if(payloadLength > MAX_PAYLOAD_LEN) {
+    if(payloadLength > maxPayloadLength_) {
       throw DL_ABORT_EX(fmt(EX_TOO_LONG_PAYLOAD, payloadLength));
     }
     currentPayloadLength_ = payloadLength;
@@ -201,7 +202,7 @@ void PeerConnection::enableEncryption
 
 void PeerConnection::presetBuffer(const unsigned char* data, size_t length)
 {
-  size_t nwrite = std::min((size_t)MAX_PAYLOAD_LEN, length);
+  size_t nwrite = std::min(maxPayloadLength_, length);
   memcpy(resbuf_, data, nwrite);
   resbufLength_ = length;
 }
@@ -221,8 +222,19 @@ ssize_t PeerConnection::sendPendingData()
 unsigned char* PeerConnection::detachBuffer()
 {
   unsigned char* detachbuf = resbuf_;
-  resbuf_ = new unsigned char[MAX_PAYLOAD_LEN];
+  resbuf_ = new unsigned char[maxPayloadLength_];
   return detachbuf;
 }
 
+void PeerConnection::reserveBuffer(size_t minSize)
+{
+  if(maxPayloadLength_ < minSize) {
+    maxPayloadLength_ = minSize;
+    unsigned char *buf = new unsigned char[maxPayloadLength_];
+    memcpy(buf, resbuf_, resbufLength_);
+    delete [] resbuf_;
+    resbuf_ = buf;
+  }
+}
+
 } // namespace aria2
diff --git a/src/PeerConnection.h b/src/PeerConnection.h
index 3da56eb4..02383023 100644
--- a/src/PeerConnection.h
+++ b/src/PeerConnection.h
@@ -59,6 +59,8 @@ private:
   SharedHandle<Peer> peer_;
   SharedHandle<SocketCore> socket_;
 
+  // Maximum payload length
+  size_t maxPayloadLength_;
   unsigned char* resbuf_;
   size_t resbufLength_;
   size_t currentPayloadLength_;
@@ -122,6 +124,15 @@ public:
   }
 
   unsigned char* detachBuffer();
+
+  // Reserves buffer at least minSize. Reallocate memory if current
+  // buffer length < minSize
+  void reserveBuffer(size_t minSize);
+
+  size_t getMaxPayloadLength()
+  {
+    return maxPayloadLength_;
+  }
 };
 
 typedef SharedHandle<PeerConnection> PeerConnectionHandle;
diff --git a/src/PeerInteractionCommand.cc b/src/PeerInteractionCommand.cc
index 6c176999..592c20d9 100644
--- a/src/PeerInteractionCommand.cc
+++ b/src/PeerInteractionCommand.cc
@@ -170,6 +170,14 @@ PeerInteractionCommand::PeerInteractionCommand
       getDownloadEngine()->setNoWait(true);
     }
   }
+  // If the number of pieces gets bigger, the length of Bitfield
+  // message payload exceeds the initial buffer capacity of
+  // PeerConnection, which is MAX_PAYLOAD_LEN.  We expand buffer as
+  // necessary so that PeerConnection can receive the Bitfield
+  // message.
+  size_t bitfieldPayloadSize =
+    1+(requestGroup_->getDownloadContext()->getNumPieces()+7)/8;
+  peerConnection->reserveBuffer(bitfieldPayloadSize);
 
   SharedHandle<DefaultBtMessageDispatcher> dispatcher
     (new DefaultBtMessageDispatcher());
diff --git a/test/Makefile.am b/test/Makefile.am
index 127bd2e2..5e328c8c 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -203,7 +203,8 @@ aria2c_SOURCES += BtAllowedFastMessageTest.cc\
 	extension_message_test_helper.h\
 	LpdMessageDispatcherTest.cc\
 	LpdMessageReceiverTest.cc\
-	Bencode2Test.cc
+	Bencode2Test.cc\
+	PeerConnectionTest.cc
 endif # ENABLE_BITTORRENT
 
 if ENABLE_METALINK
diff --git a/test/PeerConnectionTest.cc b/test/PeerConnectionTest.cc
new file mode 100644
index 00000000..d435f3b4
--- /dev/null
+++ b/test/PeerConnectionTest.cc
@@ -0,0 +1,37 @@
+#include "PeerConnection.h"
+
+#include <cstring>
+
+#include <cppunit/extensions/HelperMacros.h>
+
+#include "Peer.h"
+#include "SocketCore.h"
+
+namespace aria2 {
+
+class PeerConnectionTest:public CppUnit::TestFixture {
+
+  CPPUNIT_TEST_SUITE(PeerConnectionTest);
+  CPPUNIT_TEST(testReserveBuffer);
+  CPPUNIT_TEST_SUITE_END();
+public:
+  void testReserveBuffer();
+};
+
+CPPUNIT_TEST_SUITE_REGISTRATION(PeerConnectionTest);
+
+void PeerConnectionTest::testReserveBuffer() {
+  PeerConnection con(1, SharedHandle<Peer>(), SharedHandle<SocketCore>());
+  con.presetBuffer((unsigned char*)"foo", 3);
+  CPPUNIT_ASSERT_EQUAL((size_t)MAX_PAYLOAD_LEN, con.getMaxPayloadLength());
+  CPPUNIT_ASSERT_EQUAL((size_t)3, con.getBufferLength());
+
+  size_t newLength = 32*1024;
+  con.reserveBuffer(newLength);
+
+  CPPUNIT_ASSERT_EQUAL(newLength, con.getMaxPayloadLength());
+  CPPUNIT_ASSERT_EQUAL((size_t)3, con.getBufferLength());
+  CPPUNIT_ASSERT(memcmp("foo", con.getBuffer(), 3) == 0);
+}
+
+} // namespace aria2