diff --git a/src/BtPieceMessageValidator.cc b/src/BtPieceMessageValidator.cc
index e1f5be5d..4b5ef38b 100644
--- a/src/BtPieceMessageValidator.cc
+++ b/src/BtPieceMessageValidator.cc
@@ -39,7 +39,7 @@
 namespace aria2 {
 
 BtPieceMessageValidator::BtPieceMessageValidator
-(const BtPieceMessage* message, size_t numPiece, size_t pieceLength)
+(const BtPieceMessage* message, size_t numPiece, int32_t pieceLength)
   : message_(message),
     numPiece_(numPiece),
     pieceLength_(pieceLength)
diff --git a/src/BtPieceMessageValidator.h b/src/BtPieceMessageValidator.h
index 30f065d8..1f24fdab 100644
--- a/src/BtPieceMessageValidator.h
+++ b/src/BtPieceMessageValidator.h
@@ -45,11 +45,11 @@ class BtPieceMessageValidator : public BtMessageValidator {
 private:
   const BtPieceMessage* message_;
   size_t numPiece_;
-  size_t pieceLength_;
+  int32_t pieceLength_;
 public:
   BtPieceMessageValidator(const BtPieceMessage* message,
                           size_t numPiece,
-                          size_t pieceLength);
+                          int32_t pieceLength);
 
   ~BtPieceMessageValidator();
 
diff --git a/src/BtPortMessage.cc b/src/BtPortMessage.cc
index 27774b25..1e1f25fb 100644
--- a/src/BtPortMessage.cc
+++ b/src/BtPortMessage.cc
@@ -87,7 +87,7 @@ void BtPortMessage::doReceivedAction()
       SharedHandle<DHTTask> task = taskFactory_->createPingTask(node);
       taskQueue_->addImmediateTask(task);
     }
-    if(routingTable_->countBucket() == 1) {
+    if(routingTable_->getNumBucket() == 1) {
       // initiate bootstrap
       A2_LOG_INFO("Dispatch node_lookup since too few buckets.");
       taskQueue_->addImmediateTask
diff --git a/src/DHTPingTask.cc b/src/DHTPingTask.cc
index fcc0750e..75a8e3b4 100644
--- a/src/DHTPingTask.cc
+++ b/src/DHTPingTask.cc
@@ -44,7 +44,7 @@
 namespace aria2 {
 
 DHTPingTask::DHTPingTask
-(const SharedHandle<DHTNode>& remoteNode, size_t numMaxRetry):
+(const SharedHandle<DHTNode>& remoteNode, int numMaxRetry):
   remoteNode_(remoteNode),
   numMaxRetry_(numMaxRetry),
   numRetry_(0),
diff --git a/src/DHTPingTask.h b/src/DHTPingTask.h
index 584d74ba..63791afc 100644
--- a/src/DHTPingTask.h
+++ b/src/DHTPingTask.h
@@ -46,9 +46,9 @@ class DHTPingTask:public DHTAbstractTask {
 private:
   SharedHandle<DHTNode> remoteNode_;
 
-  size_t numMaxRetry_;
+  int numMaxRetry_;
 
-  size_t numRetry_;
+  int numRetry_;
 
   bool pingSuccessful_;
 
@@ -56,7 +56,7 @@ private:
 
   void addMessage();
 public:
-  DHTPingTask(const SharedHandle<DHTNode>& remoteNode, size_t numMaxRetry = 0);
+  DHTPingTask(const SharedHandle<DHTNode>& remoteNode, int numMaxRetry = 0);
 
   virtual ~DHTPingTask();
 
diff --git a/src/DHTReplaceNodeTask.cc b/src/DHTReplaceNodeTask.cc
index 321f5821..163102b0 100644
--- a/src/DHTReplaceNodeTask.cc
+++ b/src/DHTReplaceNodeTask.cc
@@ -82,12 +82,16 @@ void DHTReplaceNodeTask::onReceived(const DHTPingReplyMessage* message)
   setFinished(true);
 }
 
+namespace {
+const int MAX_RETRY = 2;
+} //namespace
+
 void DHTReplaceNodeTask::onTimeout(const SharedHandle<DHTNode>& node)
 {
   ++numRetry_;
   if(numRetry_ >= MAX_RETRY) {
-    A2_LOG_INFO(fmt("ReplaceNode: Ping failed %lu times. Replace %s with %s.",
-                    static_cast<unsigned long>(numRetry_),
+    A2_LOG_INFO(fmt("ReplaceNode: Ping failed %d times. Replace %s with %s.",
+                    numRetry_,
                     node->toString().c_str(),
                     newNode_->toString().c_str()));
     node->markBad();
diff --git a/src/DHTReplaceNodeTask.h b/src/DHTReplaceNodeTask.h
index b4f943c3..18e8f761 100644
--- a/src/DHTReplaceNodeTask.h
+++ b/src/DHTReplaceNodeTask.h
@@ -49,9 +49,7 @@ private:
 
   SharedHandle<DHTNode> newNode_;
 
-  static const size_t MAX_RETRY = 2;
-
-  size_t numRetry_;
+  int numRetry_;
 
   time_t timeout_;
 
diff --git a/src/DHTRoutingTable.cc b/src/DHTRoutingTable.cc
index a9fbd157..ab23a7bb 100644
--- a/src/DHTRoutingTable.cc
+++ b/src/DHTRoutingTable.cc
@@ -113,7 +113,7 @@ void DHTRoutingTable::getClosestKNodes
   dht::findClosestKNodes(nodes, root_, key);
 }
 
-size_t DHTRoutingTable::countBucket() const
+int DHTRoutingTable::getNumBucket() const
 {
   return numBucket_;
 }
diff --git a/src/DHTRoutingTable.h b/src/DHTRoutingTable.h
index 231c4034..97cc4e58 100644
--- a/src/DHTRoutingTable.h
+++ b/src/DHTRoutingTable.h
@@ -56,7 +56,7 @@ private:
 
   DHTBucketTreeNode* root_;
 
-  size_t numBucket_;
+  int numBucket_;
 
   SharedHandle<DHTTaskQueue> taskQueue_;
 
@@ -75,7 +75,7 @@ public:
   void getClosestKNodes(std::vector<SharedHandle<DHTNode> >& nodes,
                         const unsigned char* key) const;
 
-  size_t countBucket() const;
+  int getNumBucket() const;
 
   void showBuckets() const;
 
diff --git a/src/DHTTaskExecutor.cc b/src/DHTTaskExecutor.cc
index 87949110..ba57c1f3 100644
--- a/src/DHTTaskExecutor.cc
+++ b/src/DHTTaskExecutor.cc
@@ -44,7 +44,7 @@
 
 namespace aria2 {
 
-DHTTaskExecutor::DHTTaskExecutor(size_t numConcurrent)
+DHTTaskExecutor::DHTTaskExecutor(int numConcurrent)
   : numConcurrent_(numConcurrent)
 {}
 
@@ -55,7 +55,12 @@ void DHTTaskExecutor::update()
   execTasks_.erase(std::remove_if(execTasks_.begin(), execTasks_.end(),
                                   mem_fun_sh(&DHTTask::finished)),
                    execTasks_.end());
-  size_t r = numConcurrent_-execTasks_.size();
+  int r;
+  if(static_cast<size_t>(numConcurrent_) > execTasks_.size()) {
+    r = numConcurrent_-execTasks_.size();
+  } else {
+    r = 0;
+  }
   while(r && !queue_.empty()) {
     SharedHandle<DHTTask> task = queue_.front();
     queue_.pop_front();
diff --git a/src/DHTTaskExecutor.h b/src/DHTTaskExecutor.h
index f43b3dad..f64fd6c6 100644
--- a/src/DHTTaskExecutor.h
+++ b/src/DHTTaskExecutor.h
@@ -48,11 +48,11 @@ class DHTTask;
 
 class DHTTaskExecutor {
 private:
-  size_t numConcurrent_;
+  int numConcurrent_;
   std::vector<SharedHandle<DHTTask> > execTasks_;
   std::deque<SharedHandle<DHTTask> > queue_;
 public:
-  DHTTaskExecutor(size_t numConcurrent);
+  DHTTaskExecutor(int numConcurrent);
 
   ~DHTTaskExecutor();
 
@@ -68,7 +68,7 @@ public:
     return execTasks_.size();
   }
 
-  size_t getNumConcurrent() const
+  int getNumConcurrent() const
   {
     return numConcurrent_;
   }
diff --git a/src/DHTTaskFactory.h b/src/DHTTaskFactory.h
index c59f705b..d943022f 100644
--- a/src/DHTTaskFactory.h
+++ b/src/DHTTaskFactory.h
@@ -52,7 +52,7 @@ public:
 
   virtual SharedHandle<DHTTask>
   createPingTask(const SharedHandle<DHTNode>& remoteNode,
-                 size_t numRetry = 0) = 0;
+                 int numRetry = 0) = 0;
 
   virtual SharedHandle<DHTTask>
   createNodeLookupTask(const unsigned char* targetID) = 0;
diff --git a/src/DHTTaskFactoryImpl.cc b/src/DHTTaskFactoryImpl.cc
index efc9afc3..aec36c7c 100644
--- a/src/DHTTaskFactoryImpl.cc
+++ b/src/DHTTaskFactoryImpl.cc
@@ -62,7 +62,7 @@ DHTTaskFactoryImpl::~DHTTaskFactoryImpl() {}
 
 SharedHandle<DHTTask>
 DHTTaskFactoryImpl::createPingTask(const SharedHandle<DHTNode>& remoteNode,
-                                   size_t numRetry)
+                                   int numRetry)
 {
   SharedHandle<DHTPingTask> task(new DHTPingTask(remoteNode, numRetry));
   task->setTimeout(timeout_);
diff --git a/src/DHTTaskFactoryImpl.h b/src/DHTTaskFactoryImpl.h
index 5adab80b..d383cf18 100644
--- a/src/DHTTaskFactoryImpl.h
+++ b/src/DHTTaskFactoryImpl.h
@@ -69,7 +69,7 @@ public:
 
   virtual SharedHandle<DHTTask>
   createPingTask(const SharedHandle<DHTNode>& remoteNode,
-                 size_t numRetry = 0);
+                 int numRetry = 0);
 
   virtual SharedHandle<DHTTask>
   createNodeLookupTask(const unsigned char* targetID);
diff --git a/src/FileEntry.cc b/src/FileEntry.cc
index 43a226aa..42163890 100644
--- a/src/FileEntry.cc
+++ b/src/FileEntry.cc
@@ -149,7 +149,7 @@ FileEntry::getRequest
         if(req->setUri(uri)) {
           if(std::count(inFlightHosts.begin(),
                         inFlightHosts.end(),req->getHost())
-             >= static_cast<int>(maxConnectionPerServer_)) {
+             >= maxConnectionPerServer_) {
             pending.push_back(uri);
             ignoreHost.push_back(req->getHost());
             req.reset();
@@ -250,10 +250,10 @@ FileEntry::findFasterRequest
       continue;
     }
     if(std::count(inFlightHosts.begin(), inFlightHosts.end(),us.host)
-       >= static_cast<int>(maxConnectionPerServer_)) {
+       >= maxConnectionPerServer_) {
       A2_LOG_DEBUG(fmt("%s has already used %d times, not considered.",
                        (*i).c_str(),
-                       static_cast<int>(maxConnectionPerServer_)));
+                       maxConnectionPerServer_));
       continue;
     }
     if(findSecond(usedHosts.begin(), usedHosts.end(), us.host) !=
diff --git a/src/FileEntry.h b/src/FileEntry.h
index 1f3385ba..f698f1ba 100644
--- a/src/FileEntry.h
+++ b/src/FileEntry.h
@@ -71,7 +71,7 @@ private:
   // available.
   std::deque<URIResult> uriResults_;
   bool uniqueProtocol_;
-  size_t maxConnectionPerServer_;
+  int maxConnectionPerServer_;
   std::string originalName_;
   Timer lastFasterReplace_;
 
@@ -214,12 +214,12 @@ public:
   void extractURIResult
   (std::deque<URIResult>& res, error_code::Value r);
 
-  void setMaxConnectionPerServer(size_t n)
+  void setMaxConnectionPerServer(int n)
   {
     maxConnectionPerServer_ = n;
   }
 
-  size_t getMaxConnectionPerServer() const
+  int getMaxConnectionPerServer() const
   {
     return maxConnectionPerServer_;
   }
diff --git a/src/MSEHandshake.h b/src/MSEHandshake.h
index 2d3ea0d1..aa8aaf77 100644
--- a/src/MSEHandshake.h
+++ b/src/MSEHandshake.h
@@ -68,13 +68,13 @@ public:
   };
 
 private:
-  static const size_t PRIME_BITS = 768;
-  static const size_t KEY_LENGTH = (PRIME_BITS+7)/8;
-  static const size_t VC_LENGTH = 8;
+  static const size_t PRIME_BITS = 768U;
+  static const size_t KEY_LENGTH = (PRIME_BITS+7U)/8U;
+  static const size_t VC_LENGTH = 8U;
   // The largest buffering occurs when receiver receives step2
   // handshake.  We believe that IA is less than or equal to
   // BtHandshakeMessage::MESSAGE_LENGTH
-  static const size_t MAX_BUFFER_LENGTH = 636;
+  static const size_t MAX_BUFFER_LENGTH = 636U;
 
   cuid_t cuid_;
   SharedHandle<SocketCore> socket_;
diff --git a/src/MultiDiskAdaptor.cc b/src/MultiDiskAdaptor.cc
index 2f815f06..17f3198d 100644
--- a/src/MultiDiskAdaptor.cc
+++ b/src/MultiDiskAdaptor.cc
@@ -241,7 +241,7 @@ void MultiDiskAdaptor::openIfNot
     //     A2_LOG_DEBUG(fmt("DiskWriterEntry: Cache MISS. offset=%s",
     //            util::itos(entry->getFileEntry()->getOffset()).c_str()));
  
-    size_t numOpened = openedDiskWriterEntries_.size();
+    int numOpened = openedDiskWriterEntries_.size();
     (entry.get()->*open)();
     if(numOpened >= maxOpenFiles_) {
       // Cache is full. 
@@ -465,7 +465,7 @@ void MultiDiskAdaptor::cutTrailingGarbage()
   }
 }
 
-void MultiDiskAdaptor::setMaxOpenFiles(size_t maxOpenFiles)
+void MultiDiskAdaptor::setMaxOpenFiles(int maxOpenFiles)
 {
   maxOpenFiles_ = maxOpenFiles;
 }
diff --git a/src/MultiDiskAdaptor.h b/src/MultiDiskAdaptor.h
index dea911f5..a981cef5 100644
--- a/src/MultiDiskAdaptor.h
+++ b/src/MultiDiskAdaptor.h
@@ -104,12 +104,12 @@ typedef std::vector<DiskWriterEntryHandle> DiskWriterEntries;
 class MultiDiskAdaptor : public DiskAdaptor {
   friend class MultiFileAllocationIterator;
 private:
-  size_t pieceLength_;
+  int32_t pieceLength_;
   DiskWriterEntries diskWriterEntries_;
 
   std::vector<SharedHandle<DiskWriterEntry> > openedDiskWriterEntries_;
 
-  size_t maxOpenFiles_;
+  int maxOpenFiles_;
 
   bool readOnly_;
 
@@ -118,7 +118,7 @@ private:
   void openIfNot(const SharedHandle<DiskWriterEntry>& entry,
                  void (DiskWriterEntry::*f)());
  
-  static const size_t DEFAULT_MAX_OPEN_FILES = 100;
+  static const int DEFAULT_MAX_OPEN_FILES = 100;
 
 public:
   MultiDiskAdaptor();
@@ -149,18 +149,18 @@ public:
 
   virtual bool isReadOnlyEnabled() const { return readOnly_; }
 
-  void setPieceLength(size_t pieceLength)
+  void setPieceLength(int32_t pieceLength)
   {
     pieceLength_ = pieceLength;
   }
 
-  size_t getPieceLength() const {
+  int32_t getPieceLength() const {
     return pieceLength_;
   }
 
   virtual void cutTrailingGarbage();
 
-  void setMaxOpenFiles(size_t maxOpenFiles);
+  void setMaxOpenFiles(int maxOpenFiles);
 
   virtual size_t utime(const Time& actime, const Time& modtime);
 
diff --git a/src/RequestGroupMan.cc b/src/RequestGroupMan.cc
index 2ed3d8c4..34e9e127 100644
--- a/src/RequestGroupMan.cc
+++ b/src/RequestGroupMan.cc
@@ -560,10 +560,10 @@ void RequestGroupMan::closeFile()
 
 RequestGroupMan::DownloadStat RequestGroupMan::getDownloadStat() const
 {
-  size_t finished = 0;
-  size_t error = removedErrorResult_;
-  size_t inprogress = 0;
-  size_t removed = 0;
+  int finished = 0;
+  int error = removedErrorResult_;
+  int inprogress = 0;
+  int removed = 0;
   error_code::Value lastError = removedLastErrorResult_;
   for(std::deque<SharedHandle<DownloadResult> >::const_iterator itr =
         downloadResults_.begin(), eoi = downloadResults_.end();
@@ -850,7 +850,7 @@ void RequestGroupMan::addDownloadResult(const SharedHandle<DownloadResult>& dr)
       ++removedErrorResult_;
     }
   } else {
-    size_t curSize = downloadResults_.size();
+    int curSize = downloadResults_.size();
     if(curSize >= maxDownloadResult_) {
       std::deque<SharedHandle<DownloadResult> >::iterator last =
         downloadResults_.begin()+curSize-maxDownloadResult_+1;
diff --git a/src/RequestGroupMan.h b/src/RequestGroupMan.h
index 26e68655..fbac4276 100644
--- a/src/RequestGroupMan.h
+++ b/src/RequestGroupMan.h
@@ -78,12 +78,12 @@ private:
 
   // The number of error DownloadResult removed because of upper limit
   // of the queue
-  size_t removedErrorResult_;
+  int removedErrorResult_;
 
   // The last error of removed DownloadResult
   error_code::Value removedLastErrorResult_;
 
-  size_t maxDownloadResult_;
+  int maxDownloadResult_;
 
   void formatDownloadResultFull
   (OutputFile& out,
@@ -173,18 +173,18 @@ public:
 
   class DownloadStat {
   private:
-    size_t completed_;
-    size_t error_;
-    size_t inProgress_;
-    size_t removed_;
-    size_t waiting_;
+    int completed_;
+    int error_;
+    int inProgress_;
+    int removed_;
+    int waiting_;
     error_code::Value lastErrorResult_;
   public:
-    DownloadStat(size_t completed,
-                 size_t error,
-                 size_t inProgress,
-                 size_t removed,
-                 size_t waiting,
+    DownloadStat(int completed,
+                 int error,
+                 int inProgress,
+                 int removed,
+                 int waiting,
                  error_code::Value lastErrorResult =
                  error_code::FINISHED):
       completed_(completed),
@@ -204,7 +204,7 @@ public:
       return error_ == 0 && inProgress_ == 0 && waiting_ == 0;
     }
 
-    size_t getInProgress() const
+    int getInProgress() const
     {
       return inProgress_;
     }
@@ -305,7 +305,7 @@ public:
     return serverStatMan_;
   }
 
-  void setMaxDownloadResult(size_t v)
+  void setMaxDownloadResult(int v)
   {
     maxDownloadResult_ = v;
   }
diff --git a/src/RpcMethodImpl.h b/src/RpcMethodImpl.h
index 46c42394..fb1cccc1 100644
--- a/src/RpcMethodImpl.h
+++ b/src/RpcMethodImpl.h
@@ -331,11 +331,11 @@ private:
   template<typename InputIterator>
   std::pair<InputIterator, InputIterator>
   getPaginationRange
-  (ssize_t offset, size_t num, InputIterator first, InputIterator last)
+  (int offset, int num, InputIterator first, InputIterator last)
   {
-    size_t size = std::distance(first, last);
+    int size = std::distance(first, last);
     if(offset < 0) {
-      ssize_t tempoffset = offset+size;
+      int tempoffset = offset+size;
       if(tempoffset < 0) {
         return std::make_pair(last, last);
       }
@@ -344,10 +344,10 @@ private:
         offset = 0;
         num = tempoffset+1;
       }
-    } else if(size <= (size_t)offset) {
+    } else if(size <= offset) {
       return std::make_pair(last, last);
     }
-    size_t lastDistance;
+    int lastDistance;
     if(size < offset+num) {
       lastDistance = size;
     } else {
@@ -369,8 +369,8 @@ protected:
     if(numParam->i() < 0) {
       throw DL_ABORT_EX("The parameter num must be zero or positive integer.");
     }
-    ssize_t offset = offsetParam->i();
-    size_t num = numParam->i();
+    int offset = offsetParam->i();
+    int num = numParam->i();
     std::vector<std::string> keys;
     toStringList(std::back_inserter(keys), keysParam);
     const std::deque<SharedHandle<T> >& items = getItems(e);
diff --git a/test/BittorrentHelperTest.cc b/test/BittorrentHelperTest.cc
index 23ab3b59..277b44ba 100644
--- a/test/BittorrentHelperTest.cc
+++ b/test/BittorrentHelperTest.cc
@@ -175,12 +175,12 @@ void BittorrentHelperTest::testGetFileEntries() {
                        fileEntry1->getPath());
   CPPUNIT_ASSERT_EQUAL(std::string("aria2-test/aria2/src/aria2c"),
                        fileEntry1->getOriginalName());
-  CPPUNIT_ASSERT_EQUAL((size_t)10, fileEntry1->getMaxConnectionPerServer());
+  CPPUNIT_ASSERT_EQUAL(10, fileEntry1->getMaxConnectionPerServer());
   itr++;
   SharedHandle<FileEntry> fileEntry2 = *itr;
   CPPUNIT_ASSERT_EQUAL(std::string("./aria2-test/aria2-0.2.2.tar.bz2"),
                        fileEntry2->getPath());
-  CPPUNIT_ASSERT_EQUAL((size_t)10, fileEntry2->getMaxConnectionPerServer());
+  CPPUNIT_ASSERT_EQUAL(10, fileEntry2->getMaxConnectionPerServer());
 }
 
 void BittorrentHelperTest::testGetFileEntriesSingle() {
@@ -198,7 +198,7 @@ void BittorrentHelperTest::testGetFileEntriesSingle() {
                        fileEntry1->getPath());
   CPPUNIT_ASSERT_EQUAL(std::string("aria2-0.8.2.tar.bz2"),
                        fileEntry1->getOriginalName());
-  CPPUNIT_ASSERT_EQUAL((size_t)10, fileEntry1->getMaxConnectionPerServer());
+  CPPUNIT_ASSERT_EQUAL(10, fileEntry1->getMaxConnectionPerServer());
 }
 
 void BittorrentHelperTest::testGetTotalLength() {
diff --git a/test/BtPortMessageTest.cc b/test/BtPortMessageTest.cc
index b3223d20..6d6a9446 100644
--- a/test/BtPortMessageTest.cc
+++ b/test/BtPortMessageTest.cc
@@ -40,7 +40,7 @@ public:
   class MockDHTTaskFactory2:public MockDHTTaskFactory {
   public:
     virtual SharedHandle<DHTTask>
-    createPingTask(const SharedHandle<DHTNode>& remoteNode, size_t numRetry)
+    createPingTask(const SharedHandle<DHTNode>& remoteNode, int numRetry)
     {
       return SharedHandle<DHTTask>(new MockDHTTask(remoteNode));
     }
diff --git a/test/MockDHTTaskFactory.h b/test/MockDHTTaskFactory.h
index fee36193..1f40ae7f 100644
--- a/test/MockDHTTaskFactory.h
+++ b/test/MockDHTTaskFactory.h
@@ -11,14 +11,7 @@ public:
 
   virtual SharedHandle<DHTTask>
   createPingTask(const SharedHandle<DHTNode>& remoteNode,
-                 size_t numRetry = 0)
-  {
-    return SharedHandle<DHTTask>();
-  }
-
-  virtual SharedHandle<DHTTask>
-  createGetIDTask(const SharedHandle<DHTNode>& remoteNode,
-                  size_t numRetry = 0)
+                 int numRetry = 0)
   {
     return SharedHandle<DHTTask>();
   }