diff --git a/ChangeLog b/ChangeLog
index 37e36f2248..f3c5fc94bb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Nov 12 02:10:08 2005  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* configure.in, eval.c, intern.h: check fd_mask type.
+
 Fri Nov 11 19:53:47 2005  Hirokazu Yamamoto  <ocean@m2.ccsnet.ne.jp>
 
 	* eval.c, intern.h: failed to compile where NFDBITS is defined but
diff --git a/configure.in b/configure.in
index 65fd015b3e..687e9e833f 100644
--- a/configure.in
+++ b/configure.in
@@ -476,6 +476,8 @@ AC_STRUCT_ST_BLKSIZE
 AC_STRUCT_ST_BLOCKS
 AC_STRUCT_ST_RDEV
 
+AC_CHECK_TYPE(fd_mask, [AC_DEFINE(HAVE_RB_FD_INIT, 1)])
+
 AC_CACHE_CHECK(for stack end address, rb_cv_stack_end_address,
 [rb_cv_stack_end_address=no
 for addr in __libc_stack_end _SEND; do
diff --git a/eval.c b/eval.c
index fd7a209aff..98e60a4261 100644
--- a/eval.c
+++ b/eval.c
@@ -9546,7 +9546,7 @@ enum thread_status {
 # endif
 #endif
 
-#if defined(NFDBITS) && defined(howmany)
+#if defined(NFDBITS) && defined(HAVE_RB_FD_INIT)
 void
 rb_fd_init(fds)
     volatile rb_fdset_t *fds;
diff --git a/intern.h b/intern.h
index 31602598f6..c2adeb398d 100644
--- a/intern.h
+++ b/intern.h
@@ -161,14 +161,12 @@ NORETURN(void rb_load_fail(const char*));
 NORETURN(void rb_error_frozen(const char*));
 void rb_check_frozen(VALUE);
 /* eval.c */
-#if defined(NFDBITS) && defined(howmany)
+#if defined(NFDBITS) && defined(HAVE_RB_FD_INIT)
 typedef struct {
     int maxfd;
     fd_set *fdset;
 } rb_fdset_t;
 
-#define HAVE_RB_FD_INIT 1
-
 void rb_fd_init(volatile rb_fdset_t *);
 void rb_fd_term(rb_fdset_t *);
 void rb_fd_zero(rb_fdset_t *);