diff --git a/ChangeLog b/ChangeLog
index cca296819d..ebeaf27539 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Oct 18 10:42:19 2015  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* ruby.c (open_load_file): add a comment.
+
 Sun Oct 18 10:12:46 2015  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* file.c (rb_file_identical_p): simplify ifdefs
diff --git a/ruby.c b/ruby.c
index 5c17f409c8..b0fee645c3 100644
--- a/ruby.c
+++ b/ruby.c
@@ -1778,6 +1778,10 @@ open_load_file(VALUE fname_v, int *xflag)
 		rb_load_fail(fname_v, strerror(e));
 	    }
 	    if (S_ISFIFO(st.st_mode)) {
+		/*
+		  We need to wait if FIFO is empty. It's FIFO's semantics.
+		  rb_thread_wait_fd() release GVL. So, it's safe.
+		*/
 		rb_thread_wait_fd(fd);
 	    }
 	}