diff --git a/thread.c b/thread.c
index 7b8d87ca79..6181a75ae6 100644
--- a/thread.c
+++ b/thread.c
@@ -3965,6 +3965,15 @@ rb_thread_fd_select(int max, rb_fdset_t * read, rb_fdset_t * write, rb_fdset_t *
 	return 0;
     }
 
+    if (read) {
+	rb_fd_resize(max - 1, read);
+    }
+    if (write) {
+	rb_fd_resize(max - 1, write);
+    }
+    if (except) {
+	rb_fd_resize(max - 1, except);
+    }
     return do_select(max, read, write, except, timeout);
 }