diff --git a/src/fileio.c b/src/fileio.c
index 55397d7..a1c14c9 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -86,6 +86,7 @@ void TIDY_CALL TY_(filesink_putByte)( void* sinkData, byte bv )
   FILE* fout = (FILE*) sinkData;
   fputc( bv, fout );
 #if !defined(NDEBUG) && defined(_MSC_VER)
+  if (fout->_file != 2)
     SPRTF("%c",bv);
 #endif
 }