diff --git a/src/ChunkedDecoder.cc b/src/ChunkedDecoder.cc
index 9ec6872a..1404348b 100644
--- a/src/ChunkedDecoder.cc
+++ b/src/ChunkedDecoder.cc
@@ -49,7 +49,7 @@ ChunkedDecoder::~ChunkedDecoder() {}
 
 void ChunkedDecoder::init() {}
 
-static bool readChunkSize(size_t& chunkSize, std::string& in)
+static bool readChunkSize(uint64_t& chunkSize, std::string& in)
 {
   std::string::size_type crlfPos = in.find(A2STR::CRLF);
   if(crlfPos == std::string::npos) {
@@ -59,14 +59,14 @@ static bool readChunkSize(size_t& chunkSize, std::string& in)
   if(extPos == std::string::npos || crlfPos < extPos) {
     extPos = crlfPos;
   }
-  chunkSize = Util::parseUInt(in.substr(0, extPos), 16);
+  chunkSize = Util::parseULLInt(in.substr(0, extPos), 16);
   in.erase(0, crlfPos+2);
   return true;
 }
 
-static bool readData(std::string& out, size_t& chunkSize, std::string& in)
+static bool readData(std::string& out, uint64_t& chunkSize, std::string& in)
 {
-  size_t readlen = std::min(chunkSize, in.size());
+  uint64_t readlen = std::min(chunkSize, static_cast<uint64_t>(in.size()));
   out.append(in.begin(), in.begin()+readlen);
   in.erase(0, readlen);
   chunkSize -= readlen;
@@ -94,10 +94,6 @@ std::string ChunkedDecoder::decode(const unsigned char* inbuf, size_t inlen)
 	  _state = STREAM_END;
 	  break;
 	} else {
-	  if(_chunkSize > MAX_CHUNK_SIZE) {
-	    throw DlAbortEx
-	      (StringFormat(EX_TOO_LARGE_CHUNK, _chunkSize).str());
-	  }
 	  _state = READ_DATA;
 	}
       } else {
diff --git a/src/ChunkedDecoder.h b/src/ChunkedDecoder.h
index e5b58edb..6aa5d1f2 100644
--- a/src/ChunkedDecoder.h
+++ b/src/ChunkedDecoder.h
@@ -49,12 +49,10 @@ private:
 
   std::string _buf;
 
-  size_t _chunkSize;
+  uint64_t _chunkSize;
 
   STATE _state;
   
-  static const size_t MAX_CHUNK_SIZE = 1024*1024;
-
   static const std::string NAME;
 
 public:
diff --git a/test/ChunkedDecoderTest.cc b/test/ChunkedDecoderTest.cc
index 84234abe..dd1b1c2b 100644
--- a/test/ChunkedDecoderTest.cc
+++ b/test/ChunkedDecoderTest.cc
@@ -110,16 +110,24 @@ void ChunkedDecoderTest::testDecode()
 
 void ChunkedDecoderTest::testDecode_tooLargeChunkSize()
 {
-  // Feed chunkSize == ChunkedDecoder::MAX_CHUNK_SIZE + 1 == 0x100001.
-  std::basic_string<unsigned char> msg =
-    reinterpret_cast<const unsigned char*>("100001\r\n");
-
-  ChunkedDecoder decoder;
-  try {
+  // chunkSize should be under 2^64-1
+  {
+    std::basic_string<unsigned char> msg =
+      reinterpret_cast<const unsigned char*>("ffffffffffffffff\r\n");
+    ChunkedDecoder decoder;
     decoder.decode(msg.c_str(), msg.size());
-    CPPUNIT_FAIL("exception must be thrown.");
-  } catch(DlAbortEx& e) {
-    // success
+  }
+  // chunkSize 2^64 causes error
+  {
+    std::basic_string<unsigned char> msg =
+      reinterpret_cast<const unsigned char*>("10000000000000000\r\n");
+    ChunkedDecoder decoder;
+    try {
+      decoder.decode(msg.c_str(), msg.size());
+      CPPUNIT_FAIL("exception must be thrown.");
+    } catch(DlAbortEx& e) {
+      // success
+    }
   }
 }