diff --git a/lang/cem/libcc.ansi/stdio/vsprintf.c b/lang/cem/libcc.ansi/stdio/vsprintf.c
index 3cd5cb184..52378b858 100644
--- a/lang/cem/libcc.ansi/stdio/vsprintf.c
+++ b/lang/cem/libcc.ansi/stdio/vsprintf.c
@@ -14,7 +14,7 @@ vsprintf(char *s, const char *format, va_list arg)
 	FILE tmp_stream;
 
 	tmp_stream._fd     = -1;
-	tmp_stream._flags  = _IOWRITE + _IONBF;
+	tmp_stream._flags  = _IOWRITE + _IONBF + _IOWRITING;
 	tmp_stream._buf    = (unsigned char *) s;
 	tmp_stream._ptr    = (unsigned char *) s;
 	tmp_stream._count  = 32767;