diff --git a/jupyter_notebook/static/services/sessions/session.js b/jupyter_notebook/static/services/sessions/session.js
index 923558df6..8eeaaf21c 100644
--- a/jupyter_notebook/static/services/sessions/session.js
+++ b/jupyter_notebook/static/services/sessions/session.js
@@ -121,6 +121,7 @@ define([
             cache: false,
             type: "POST",
             data: JSON.stringify(this._get_model()),
+            contentType: 'application/json',
             dataType: "json",
             success: this._on_success(on_success),
             error: this._on_error(on_error)
@@ -168,6 +169,7 @@ define([
             cache: false,
             type: "PATCH",
             data: JSON.stringify(this._get_model()),
+            contentType: 'application/json',
             dataType: "json",
             success: this._on_success(success),
             error: this._on_error(error)