diff --git a/ChangeLog b/ChangeLog
index 83e043c7..7f74e174 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2010-05-08  Tatsuhiro Tsujikawa  <t-tujikawa@users.sourceforge.net>
+
+	Return const reference.
+	* src/DefaultPieceStorage.h
+	* src/DownloadContext.h
+	* src/FeatureConfig.cc
+	* src/FeatureConfig.h
+	* src/OptionParser.cc
+	* src/OptionParser.h
+	* src/SimpleRandomizer.cc
+	* src/SimpleRandomizer.h
+
 2010-05-07  Tatsuhiro Tsujikawa  <t-tujikawa@users.sourceforge.net>
 
 	Bump up version number to 1.9.3.
diff --git a/src/DefaultPieceStorage.h b/src/DefaultPieceStorage.h
index 01ed976d..bf4da0ba 100644
--- a/src/DefaultPieceStorage.h
+++ b/src/DefaultPieceStorage.h
@@ -243,7 +243,7 @@ public:
     _pieceSelector = pieceSelector;
   }
 
-  SharedHandle<PieceSelector> getPieceSelector() const
+  const SharedHandle<PieceSelector>& getPieceSelector() const
   {
     return _pieceSelector;
   }
diff --git a/src/DownloadContext.h b/src/DownloadContext.h
index 692ca052..563a601d 100644
--- a/src/DownloadContext.h
+++ b/src/DownloadContext.h
@@ -201,7 +201,7 @@ public:
 
   void setDir(const std::string& dir) { _dir = dir; }
 
-  SharedHandle<Signature> getSignature() const { return _signature; }
+  const SharedHandle<Signature>& getSignature() const { return _signature; }
 
   void setSignature(const SharedHandle<Signature>& signature)
   {
diff --git a/src/FeatureConfig.cc b/src/FeatureConfig.cc
index 6f93449a..cdf2022c 100644
--- a/src/FeatureConfig.cc
+++ b/src/FeatureConfig.cc
@@ -120,7 +120,7 @@ FeatureConfig::FeatureConfig() {
   _features.insert(vbegin(featureArray), vend(featureArray));
 }
 
-SharedHandle<FeatureConfig> FeatureConfig::getInstance()
+const SharedHandle<FeatureConfig>& FeatureConfig::getInstance()
 {
   if(_featureConfig.isNull()) {
     _featureConfig.reset(new FeatureConfig());
diff --git a/src/FeatureConfig.h b/src/FeatureConfig.h
index 0877ecb3..05ef542e 100644
--- a/src/FeatureConfig.h
+++ b/src/FeatureConfig.h
@@ -56,7 +56,7 @@ private:
 
   FeatureConfig();
 public:
-  static SharedHandle<FeatureConfig> getInstance();
+  static const SharedHandle<FeatureConfig>& getInstance();
 
   uint16_t getDefaultPort(const std::string& protocol) const;
 
diff --git a/src/OptionParser.cc b/src/OptionParser.cc
index 5508dc8a..9553ecf9 100644
--- a/src/OptionParser.cc
+++ b/src/OptionParser.cc
@@ -369,7 +369,7 @@ SharedHandle<OptionHandler> OptionParser::findByShortName(char shortName) const
 
 SharedHandle<OptionParser> OptionParser::_optionParser;
 
-SharedHandle<OptionParser> OptionParser::getInstance()
+const SharedHandle<OptionParser>& OptionParser::getInstance()
 {
   if(_optionParser.isNull()) {
     _optionParser.reset(new OptionParser());
diff --git a/src/OptionParser.h b/src/OptionParser.h
index 8294d3ed..1abf7167 100644
--- a/src/OptionParser.h
+++ b/src/OptionParser.h
@@ -101,7 +101,7 @@ public:
   // Hidden options are not returned.
   SharedHandle<OptionHandler> findByShortName(char shortName) const;
 
-  static SharedHandle<OptionParser> getInstance();
+  static const SharedHandle<OptionParser>& getInstance();
 };
 
 typedef SharedHandle<OptionParser> OptionParserHandle;
diff --git a/src/SimpleRandomizer.cc b/src/SimpleRandomizer.cc
index b0fcb98c..2f7d8504 100644
--- a/src/SimpleRandomizer.cc
+++ b/src/SimpleRandomizer.cc
@@ -42,7 +42,7 @@ namespace aria2 {
 
 SharedHandle<SimpleRandomizer> SimpleRandomizer::_randomizer;
 
-SharedHandle<SimpleRandomizer> SimpleRandomizer::getInstance()
+const SharedHandle<SimpleRandomizer>& SimpleRandomizer::getInstance()
 {
   if(_randomizer.isNull()) {
     _randomizer.reset(new SimpleRandomizer());
diff --git a/src/SimpleRandomizer.h b/src/SimpleRandomizer.h
index 5bf32929..cbecaf6a 100644
--- a/src/SimpleRandomizer.h
+++ b/src/SimpleRandomizer.h
@@ -46,7 +46,7 @@ private:
   SimpleRandomizer();
 public:
   
-  static SharedHandle<SimpleRandomizer> getInstance();
+  static const SharedHandle<SimpleRandomizer>& getInstance();
   
   static void init();