diff --git a/ChangeLog b/ChangeLog
index b97b139dd6..112c5d1c43 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Tue May 11 14:09:21 2010  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* win32/win32.c, include/ruby/win32.h (rb_w32_has_cancel_io): new
+	  function.
+
+	* io.c (WAIT_FD_IN_WIN32): check only when it's not cancelable.
+
 Tue May 11 11:49:44 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/sdbm/sdbm.h (DBM): large file support on win32.
diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index d75c7ea9d3..47a85270a5 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -222,6 +222,7 @@ struct msghdr {
 extern int    rb_w32_cmdvector(const char *, char ***);
 extern rb_pid_t  rb_w32_pipe_exec(const char *, const char *, int, int *, int *);
 extern int    flock(int fd, int oper);
+extern int    rb_w32_has_cancel_io(void);
 extern int    rb_w32_is_socket(int);
 extern int    WSAAPI rb_w32_accept(int, struct sockaddr *, int *);
 extern int    WSAAPI rb_w32_bind(int, const struct sockaddr *, int);
diff --git a/io.c b/io.c
index eccc93b141..00ec9ffdb4 100644
--- a/io.c
+++ b/io.c
@@ -189,9 +189,10 @@ static int max_file_descriptor = NOFILE;
 #define READ_CHAR_PENDING(fptr) ((fptr)->cbuf_len)
 
 #if defined(_WIN32)
-#define WAIT_FD_IN_WIN32(fptr) rb_thread_wait_fd((fptr)->fd);
+#define WAIT_FD_IN_WIN32(fptr) \
+    (rb_w32_has_cancel_io() ? 0 : rb_thread_wait_fd((fptr)->fd))
 #else
-#define WAIT_FD_IN_WIN32(fptr) ;
+#define WAIT_FD_IN_WIN32(fptr)
 #endif
 
 #define READ_CHECK(fptr) do {\
diff --git a/win32/win32.c b/win32/win32.c
index 5b05510209..fa49cf17de 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -548,6 +548,12 @@ init_env(void)
 typedef BOOL (WINAPI *cancel_io_t)(HANDLE);
 static cancel_io_t cancel_io = NULL;
 
+int
+rb_w32_has_cancel_io(void)
+{
+    return cancel_io != NULL;
+}
+
 static void
 init_func(void)
 {