diff --git a/godoc/static/playground.js b/godoc/static/playground.js
index bea9c4b..51b00a4 100644
--- a/godoc/static/playground.js
+++ b/godoc/static/playground.js
@@ -403,6 +403,7 @@
         processData: false,
         data: sharingData,
         type: "POST",
+        contentType: "text/plain; charset=utf-8",
         complete: function(xhr) {
           sharing = false;
           if (xhr.status != 200) {
diff --git a/godoc/static/static.go b/godoc/static/static.go
index 8197d89..0711e51 100644
--- a/godoc/static/static.go
+++ b/godoc/static/static.go
@@ -1,4 +1,4 @@
-// Copyright 2017 The Go Authors. All rights reserved.
+// Copyright 2018 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -2599,6 +2599,7 @@
         processData: false,
         data: sharingData,
         type: "POST",
+        contentType: "text/plain; charset=utf-8",
         complete: function(xhr) {
           sharing = false;
           if (xhr.status != 200) {