diff --git a/tensorboard/plugins/custom_scalar/BUILD b/tensorboard/plugins/custom_scalar/BUILD
index b6177be636..723f8791e1 100644
--- a/tensorboard/plugins/custom_scalar/BUILD
+++ b/tensorboard/plugins/custom_scalar/BUILD
@@ -78,11 +78,13 @@ py_test(
         ":summary",
         "//tensorboard:expect_numpy_installed",
         "//tensorboard:expect_tensorflow_installed",
+        "//tensorboard/backend:application",
         "//tensorboard/backend/event_processing:event_multiplexer",
         "//tensorboard/plugins:base_plugin",
         "//tensorboard/plugins/scalar:scalars_plugin",
         "//tensorboard/plugins/scalar:summary",
         "//tensorboard/util:test_util",
+        "@org_pocoo_werkzeug",
     ],
 )
 
@@ -99,12 +101,14 @@ py_test(
         ":summary",
         "//tensorboard:expect_numpy_installed",
         "//tensorboard:expect_tensorflow_installed",
+        "//tensorboard/backend:application",
         "//tensorboard/backend/event_processing:event_multiplexer",
         "//tensorboard/compat:no_tensorflow",
         "//tensorboard/plugins:base_plugin",
         "//tensorboard/plugins/scalar:scalars_plugin",
         "//tensorboard/plugins/scalar:summary",
         "//tensorboard/util:test_util",
+        "@org_pocoo_werkzeug",
     ],
 )
 
diff --git a/tensorboard/plugins/custom_scalar/custom_scalars_plugin.py b/tensorboard/plugins/custom_scalar/custom_scalars_plugin.py
index 8db3619500..2deefdc268 100644
--- a/tensorboard/plugins/custom_scalar/custom_scalars_plugin.py
+++ b/tensorboard/plugins/custom_scalar/custom_scalars_plugin.py
@@ -121,9 +121,12 @@ def frontend_metadata(self):
     def download_data_route(self, request):
         run = request.args.get("run")
         tag = request.args.get("tag")
+        experiment = plugin_util.experiment_id(request.environ)
         response_format = request.args.get("format")
         try:
-            body, mime_type = self.download_data_impl(run, tag, response_format)
+            body, mime_type = self.download_data_impl(
+                run, tag, experiment, response_format
+            )
         except ValueError as e:
             return http_util.Respond(
                 request=request,
diff --git a/tensorboard/plugins/custom_scalar/custom_scalars_plugin_test.py b/tensorboard/plugins/custom_scalar/custom_scalars_plugin_test.py
index 15c74afb25..3807e575d2 100644
--- a/tensorboard/plugins/custom_scalar/custom_scalars_plugin_test.py
+++ b/tensorboard/plugins/custom_scalar/custom_scalars_plugin_test.py
@@ -19,12 +19,18 @@
 from __future__ import division
 from __future__ import print_function
 
+import csv
+import io
+import json
 import os
 
 import numpy as np
 import tensorflow as tf
+from werkzeug import test as werkzeug_test
+from werkzeug import wrappers
 
 from google.protobuf import json_format
+from tensorboard.backend import application
 from tensorboard.backend.event_processing import (
     plugin_event_multiplexer as event_multiplexer,
 )
@@ -176,11 +182,16 @@ def createPlugin(self, logdir):
             ] = plugin_instance
         return custom_scalars_plugin_instance
 
-    def testDownloadData(self):
-        body, mime_type = self.plugin.download_data_impl(
-            "foo", "squares/scalar_summary", "exp_id", "json"
+    def test_download_url_json(self):
+        wsgi_app = application.TensorBoardWSGI([self.plugin])
+        server = werkzeug_test.Client(wsgi_app, wrappers.BaseResponse)
+        response = server.get(
+            "/data/plugin/custom_scalars/download_data?run=%s&tag=%s"
+            % ("foo", "squares/scalar_summary")
         )
-        self.assertEqual("application/json", mime_type)
+        self.assertEqual(200, response.status_code)
+        self.assertEqual("application/json", response.headers["Content-Type"])
+        body = json.loads(response.get_data())
         self.assertEqual(4, len(body))
         for step, entry in enumerate(body):
             # The time stamp should be reasonable.
@@ -188,6 +199,23 @@ def testDownloadData(self):
             self.assertEqual(step, entry[1])
             np.testing.assert_allclose(step * step, entry[2])
 
+    def test_download_url_csv(self):
+        wsgi_app = application.TensorBoardWSGI([self.plugin])
+        server = werkzeug_test.Client(wsgi_app, wrappers.BaseResponse)
+        response = server.get(
+            "/data/plugin/custom_scalars/download_data?run=%s&tag=%s&format=csv"
+            % ("foo", "squares/scalar_summary")
+        )
+        self.assertEqual(200, response.status_code)
+        self.assertEqual(
+            "text/csv; charset=utf-8", response.headers["Content-Type"]
+        )
+        payload = response.get_data()
+        s = io.StringIO(payload.decode("utf-8"))
+        reader = csv.reader(s)
+        self.assertEqual(["Wall time", "Step", "Value"], next(reader))
+        self.assertEqual(len(list(reader)), 4)
+
     def testScalars(self):
         body = self.plugin.scalars_impl("bar", "increments", "exp_id")
         self.assertTrue(body["regex_valid"])