diff --git a/falcon/constants.py b/falcon/constants.py
index 24057f2b7..9bd71f373 100644
--- a/falcon/constants.py
+++ b/falcon/constants.py
@@ -151,6 +151,8 @@
         ('.jpeg', MEDIA_JPEG),
         ('.jpg', MEDIA_JPEG),
         ('.js', MEDIA_JS),
+        ('.json', MEDIA_JSON),
+        ('.mjs', MEDIA_JS),
         ('.png', MEDIA_PNG),
         ('.txt', MEDIA_TEXT),
         ('.xml', MEDIA_XML),
diff --git a/tests/test_response.py b/tests/test_response.py
index 1116be3a3..fe2b73d93 100644
--- a/tests/test_response.py
+++ b/tests/test_response.py
@@ -71,8 +71,14 @@ def test_response_option_mimetype_init(monkeypatch):
     ro = ResponseOptions()
 
     assert ro.static_media_types['.js'] == 'text/javascript'
+    assert ro.static_media_types['.json'] == 'application/json'
+    assert ro.static_media_types['.mjs'] == 'text/javascript'
 
     mock.reset_mock()
     mock.inited = True
     ro = ResponseOptions()
     mock.init.assert_not_called()
+
+    assert ro.static_media_types['.js'] == 'text/javascript'
+    assert ro.static_media_types['.json'] == 'application/json'
+    assert ro.static_media_types['.mjs'] == 'text/javascript'