diff --git a/src/fileio.c b/src/fileio.c
index a1c14c9..f2e11e7 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -86,7 +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)
+  if (_fileno(fout) != 2)
     SPRTF("%c",bv);
 #endif
 }