1 files changed, 1 insertions, 0 deletions
diff --git a/rubyio.h b/rubyio.h
index 377a66b719..a456fff1c5 100644
--- a/rubyio.h
+++ b/rubyio.h
@@ -59,6 +59,7 @@ FILE *rb_fopen _((const char*, const char*));
 FILE *rb_fdopen _((int, const char*));
 int rb_getc _((FILE*));
 long rb_io_fread _((char *, long, FILE *));
+long rb_io_fwrite _((const char *, long, FILE *));
 int  rb_io_mode_flags _((const char*));
 void rb_io_check_writable _((OpenFile*));
 void rb_io_check_readable _((OpenFile*));