diff --git a/src/BufferedFile.cc b/src/BufferedFile.cc
index f0096326..d1af1c09 100644
--- a/src/BufferedFile.cc
+++ b/src/BufferedFile.cc
@@ -156,13 +156,9 @@ size_t BufferedFile::transfer(std::ostream& out)
   return count;
 }
 
-int BufferedFile::printf(const char* format, ...)
+int BufferedFile::vprintf(const char* format, va_list va)
 {
-  va_list ap;
-  va_start(ap, format);
-  int r = vfprintf(fp_, format, ap);
-  va_end(ap);
-  return r;
+  return vfprintf(fp_, format, va);
 }
 
 int BufferedFile::flush()
diff --git a/src/BufferedFile.h b/src/BufferedFile.h
index 0e267f0a..f0d78e07 100644
--- a/src/BufferedFile.h
+++ b/src/BufferedFile.h
@@ -73,8 +73,7 @@ public:
   // Convenient method. Read data to end of file and write them into
   // given stream. Returns written size.
   size_t transfer(std::ostream& out);
-  // wrapper for fprintf
-  virtual int printf(const char* format, ...);
+  virtual int vprintf(const char* format, va_list va);
   // wrapper for fflush
   virtual int flush();
   virtual bool supportsColor();
diff --git a/src/NullOutputFile.h b/src/NullOutputFile.h
index c152f108..ff14ef1b 100644
--- a/src/NullOutputFile.h
+++ b/src/NullOutputFile.h
@@ -43,7 +43,7 @@ class NullOutputFile:public OutputFile {
 public:
   virtual ~NullOutputFile() {}
   virtual size_t write(const char* str) { return 0; }
-  virtual int printf(const char* format, ...) { return 0; }
+  virtual int vprintf(const char* format, va_list va) { return 0; }
   virtual int flush() { return 0; }
   virtual bool supportsColor() { return false; }
 };
diff --git a/src/OutputFile.h b/src/OutputFile.h
index ba0ccb3f..77e88991 100644
--- a/src/OutputFile.h
+++ b/src/OutputFile.h
@@ -38,6 +38,7 @@
 #include "common.h"
 
 #include <cstdlib>
+#include <cstdarg>
 
 namespace aria2 {
 
@@ -45,8 +46,15 @@ class OutputFile {
 public:
   virtual ~OutputFile() {}
   virtual size_t write(const char* str) = 0;
-  virtual int printf(const char* format, ...) = 0;
   virtual int flush() = 0;
+  virtual int vprintf(const char* format, va_list va) = 0;
+  inline int printf(const char *format, ...) {
+    va_list va;
+    va_start(va, format);
+    int rv = vprintf(format, va);
+    va_end(va);
+    return rv;
+  }
   // Returns true if the output medium supports ANSI color codes.
   virtual bool supportsColor() = 0;
 };
diff --git a/src/WinConsoleFile.cc b/src/WinConsoleFile.cc
index 0938d89d..157a2e36 100644
--- a/src/WinConsoleFile.cc
+++ b/src/WinConsoleFile.cc
@@ -72,18 +72,16 @@ size_t WinConsoleFile::write(const char* str)
   return written;
 }
 
-int WinConsoleFile::printf(const char* format, ...)
+int WinConsoleFile::vprintf(const char* format, va_list va)
 {
-  char buf[2048];
-  va_list ap;
-  va_start(ap, format);
-  int r = vsnprintf(buf, sizeof(buf), format, ap);
-  va_end(ap);
-  if(r == -1) {
-    // MINGW32 vsnprintf returns -1 if output is truncated.
-    r = strlen(buf);
-  } else if(r < 0) {
-    // Reachable?
+  ssize_t r = _vscprintf(format, va);
+  if (r <= 0) {
+    return 0;
+  }
+  char *buf = new char[++r];
+  r = vsnprintf(buf, r, format, va);
+  if (r < 0) {
+    delete [] buf;
     return 0;
   }
   DWORD written;
@@ -95,6 +93,7 @@ int WinConsoleFile::printf(const char* format, ...)
     WriteFile(GetStdHandle(stdHandle_),
               buf, r, &written, 0);
   }
+  delete [] buf;
   return written;
 }
 
diff --git a/src/WinConsoleFile.h b/src/WinConsoleFile.h
index ccd2388f..b39d292e 100644
--- a/src/WinConsoleFile.h
+++ b/src/WinConsoleFile.h
@@ -45,7 +45,7 @@ public:
   WinConsoleFile(DWORD stdHandle);
   virtual ~WinConsoleFile();
   virtual size_t write(const char* str);
-  virtual int printf(const char* format, ...);
+  virtual int vprintf(const char* format, va_list va);
   virtual int flush();
   virtual bool supportsColor();
 private: