diff --git a/ChangeLog b/ChangeLog
index c0b3b2ed..bc17d6a6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2008-05-15  Tatsuhiro Tsujikawa  <tujikawa at rednoah dot com>
+
+	Defined control file's version number as static const std::string.
+	* src/DefaultBtProgressInfoFile.cc
+	* src/DefaultBtProgressInfoFile.h
+
 2008-05-15  Tatsuhiro Tsujikawa  <tujikawa at rednoah dot com>
 
 	Use Request::METHOD_GET
diff --git a/src/DefaultBtProgressInfoFile.cc b/src/DefaultBtProgressInfoFile.cc
index 60d80130..966dcf65 100644
--- a/src/DefaultBtProgressInfoFile.cc
+++ b/src/DefaultBtProgressInfoFile.cc
@@ -58,6 +58,8 @@
 
 namespace aria2 {
 
+const std::string DefaultBtProgressInfoFile::V0000("0000");
+
 static std::string createFilename(const SharedHandle<DownloadContext>& dctx)
 {
   return dctx->getActualBasePath()+".aria2";
@@ -179,7 +181,7 @@ void DefaultBtProgressInfoFile::load()
   try {
     unsigned char version[2];
     in.read((char*)version, sizeof(version));
-    if(std::string("0000") != Util::toHex(version, sizeof(version))) {
+    if(DefaultBtProgressInfoFile::V0000 != Util::toHex(version, sizeof(version))) {
       throw DlAbortEx
 	(StringFormat("Unsupported ctrl file version: %s",
 		      Util::toHex(version, sizeof(version)).c_str()).str());
diff --git a/src/DefaultBtProgressInfoFile.h b/src/DefaultBtProgressInfoFile.h
index c7ab556c..3289017a 100644
--- a/src/DefaultBtProgressInfoFile.h
+++ b/src/DefaultBtProgressInfoFile.h
@@ -54,6 +54,7 @@ private:
 
   bool isTorrentDownload();
 
+  static const std::string V0000;
 public:
   DefaultBtProgressInfoFile(const SharedHandle<DownloadContext>& btContext,
 			    const SharedHandle<PieceStorage>& pieceStorage,