diff --git a/src/AbstractDiskWriter.cc b/src/AbstractDiskWriter.cc
index ff4f8856..f21c5261 100644
--- a/src/AbstractDiskWriter.cc
+++ b/src/AbstractDiskWriter.cc
@@ -590,4 +590,16 @@ void AbstractDiskWriter::dropCache(int64_t len, int64_t offset)
 #endif // HAVE_POSIX_FADVISE
 }
 
+void AbstractDiskWriter::flushOSBuffers()
+{
+  if (fd_ == A2_BAD_FD) {
+    return;
+  }
+#ifdef __MINGW32__
+  FlushFileBuffers(fd_);
+#else // !__MINGW32__
+  fsync(fd_);
+#endif // __MINGW32__
+}
+
 } // namespace aria2
diff --git a/src/AbstractDiskWriter.h b/src/AbstractDiskWriter.h
index 9e5c4799..96518a68 100644
--- a/src/AbstractDiskWriter.h
+++ b/src/AbstractDiskWriter.h
@@ -100,6 +100,8 @@ public:
   virtual void enableMmap() CXX11_OVERRIDE;
 
   virtual void dropCache(int64_t len, int64_t offset) CXX11_OVERRIDE;
+
+  virtual void flushOSBuffers() CXX11_OVERRIDE;
 };
 
 } // namespace aria2
diff --git a/src/AbstractSingleDiskAdaptor.cc b/src/AbstractSingleDiskAdaptor.cc
index 54ec783e..6e6b70e6 100644
--- a/src/AbstractSingleDiskAdaptor.cc
+++ b/src/AbstractSingleDiskAdaptor.cc
@@ -103,6 +103,11 @@ void AbstractSingleDiskAdaptor::writeCache(const WrDiskCacheEntry* entry)
   }
 }
 
+void AbstractSingleDiskAdaptor::flushOSBuffers()
+{
+  diskWriter_->flushOSBuffers();
+}
+
 bool AbstractSingleDiskAdaptor::fileExists()
 {
   return File(getFilePath()).exists();
diff --git a/src/AbstractSingleDiskAdaptor.h b/src/AbstractSingleDiskAdaptor.h
index 8d17686c..36899e10 100644
--- a/src/AbstractSingleDiskAdaptor.h
+++ b/src/AbstractSingleDiskAdaptor.h
@@ -72,6 +72,8 @@ public:
 
   virtual void writeCache(const WrDiskCacheEntry* entry) CXX11_OVERRIDE;
 
+  virtual void flushOSBuffers() CXX11_OVERRIDE;
+
   virtual bool fileExists() CXX11_OVERRIDE;
 
   virtual int64_t size() CXX11_OVERRIDE;
diff --git a/src/DiskAdaptor.h b/src/DiskAdaptor.h
index 2643a65d..9287b3ec 100644
--- a/src/DiskAdaptor.h
+++ b/src/DiskAdaptor.h
@@ -114,6 +114,9 @@ public:
   // Writes cached data to the underlying disk.
   virtual void writeCache(const WrDiskCacheEntry* entry) = 0;
 
+  // Force physical write of data from OS buffer cache.
+  virtual void flushOSBuffers() {};
+
   void setFileAllocationMethod(FileAllocationMethod method)
   {
     fileAllocationMethod_ = method;
diff --git a/src/DiskWriter.h b/src/DiskWriter.h
index 960e346c..03a4147b 100644
--- a/src/DiskWriter.h
+++ b/src/DiskWriter.h
@@ -85,6 +85,9 @@ public:
 
   // Drops cache in range [offset, offset + len)
   virtual void dropCache(int64_t len, int64_t offset) {}
+
+  // Force physical write of data from OS buffer cache.
+  virtual void flushOSBuffers() {}
 };
 
 } // namespace aria2
diff --git a/src/MultiDiskAdaptor.cc b/src/MultiDiskAdaptor.cc
index d4f419cf..14321aab 100644
--- a/src/MultiDiskAdaptor.cc
+++ b/src/MultiDiskAdaptor.cc
@@ -419,6 +419,17 @@ void MultiDiskAdaptor::writeCache(const WrDiskCacheEntry* entry)
   }
 }
 
+void MultiDiskAdaptor::flushOSBuffers()
+{
+  for (auto& dwent : openedDiskWriterEntries_) {
+    auto& dw = dwent->getDiskWriter();
+    if (!dw) {
+      continue;
+    }
+    dw->flushOSBuffers();
+  }
+}
+
 bool MultiDiskAdaptor::fileExists()
 {
   return std::find_if(std::begin(getFileEntries()), std::end(getFileEntries()),
diff --git a/src/MultiDiskAdaptor.h b/src/MultiDiskAdaptor.h
index 9959888a..7f8ccef4 100644
--- a/src/MultiDiskAdaptor.h
+++ b/src/MultiDiskAdaptor.h
@@ -135,6 +135,8 @@ public:
 
   virtual void writeCache(const WrDiskCacheEntry* entry) CXX11_OVERRIDE;
 
+  virtual void flushOSBuffers() CXX11_OVERRIDE;
+
   virtual bool fileExists() CXX11_OVERRIDE;
 
   virtual int64_t size() CXX11_OVERRIDE;
diff --git a/src/RequestGroup.cc b/src/RequestGroup.cc
index a008642d..fd6801fc 100644
--- a/src/RequestGroup.cc
+++ b/src/RequestGroup.cc
@@ -211,6 +211,7 @@ void RequestGroup::closeFile()
 {
   if (pieceStorage_) {
     pieceStorage_->flushWrDiskCacheEntry(true);
+    pieceStorage_->getDiskAdaptor()->flushOSBuffers();
     pieceStorage_->getDiskAdaptor()->closeFile();
   }
 }
@@ -1292,6 +1293,7 @@ void RequestGroup::saveControlFile() const
   if (saveControlFile_) {
     if (pieceStorage_) {
       pieceStorage_->flushWrDiskCacheEntry(false);
+      pieceStorage_->getDiskAdaptor()->flushOSBuffers();
     }
     progressInfoFile_->save();
   }