From 03710757efd0a0c0290b720d25333ed4d5c93228 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Tue, 4 Jun 2019 07:24:31 -0600
Subject: [PATCH] io: fix `newline` on custom output port

Closes #2677
---
 pkgs/racket-test-core/tests/racket/file.rktl | 11 +++++++++++
 racket/src/io/print/main.rkt                 |  3 +--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/pkgs/racket-test-core/tests/racket/file.rktl b/pkgs/racket-test-core/tests/racket/file.rktl
index aa43f1bbcf..b3f4eea429 100644
--- a/pkgs/racket-test-core/tests/racket/file.rktl
+++ b/pkgs/racket-test-core/tests/racket/file.rktl
@@ -1218,6 +1218,17 @@
     (test (void) close-output-port p)
     (test 10 values l)))
 
+(let ()
+  (define-struct myport (port)
+    #:property prop:output-port 0)
+  (define o (open-output-string))
+
+  (define out (make-myport o))
+  (test (void) newline out)
+  (test "\n" get-output-string o)
+
+  (err/rt-test (newline 9)))
+
 ; --------------------------------------------------
 
 (load "tmp1")
diff --git a/racket/src/io/print/main.rkt b/racket/src/io/print/main.rkt
index 3d94a4582a..b660d4a430 100644
--- a/racket/src/io/print/main.rkt
+++ b/racket/src/io/print/main.rkt
@@ -127,8 +127,7 @@
           (void))))
 
 (define/who (newline [o (current-output-port)])
-  (check who output-port? o)
-  (unsafe-write-bytes 'newline #"\n" o)
+  (unsafe-write-bytes 'newline #"\n" (->core-output-port o who))
   (void))
 
 ;; ----------------------------------------