diff --git a/app/controllers/notifications/trays_controller.rb b/app/controllers/notifications/trays_controller.rb
index 0adc0e17b..980d1ba1f 100644
--- a/app/controllers/notifications/trays_controller.rb
+++ b/app/controllers/notifications/trays_controller.rb
@@ -1,9 +1,27 @@
 class Notifications::TraysController < ApplicationController
+  MAX_ENTRIES_LIMIT = 100
+
   def show
-    @notifications = Current.user.notifications.unread.preloaded.ordered.limit(100)
+    @notifications = unread_notifications
+    if include_unread?
+      @notifications += read_notifications
+    end
 
     # Invalidate on the whole set instead of the unread set since the max updated at in the unread set
     # can stay the same when reading old notifications.
     fresh_when Current.user.notifications
   end
+
+  private
+    def unread_notifications
+      Current.user.notifications.unread.preloaded.ordered.limit(MAX_ENTRIES_LIMIT)
+    end
+
+    def read_notifications
+      Current.user.notifications.read.preloaded.ordered.limit(MAX_ENTRIES_LIMIT)
+    end
+
+    def include_unread?
+      ActiveModel::Type::Boolean.new.cast(params[:include_unread])
+    end
 end
diff --git a/test/controllers/notifications/trays_controller_test.rb b/test/controllers/notifications/trays_controller_test.rb
index d0916e305..89dc42c6f 100644
--- a/test/controllers/notifications/trays_controller_test.rb
+++ b/test/controllers/notifications/trays_controller_test.rb
@@ -18,6 +18,17 @@ class Notifications::TraysControllerTest < ActionDispatch::IntegrationTest
     get tray_notifications_path(format: :json)
 
     assert_response :success
-    assert_equal expected_ids, @response.parsed_body.map { |notification| notification["id"] }
+    assert_equal expected_ids, @response.parsed_body.map { |s| s["id"] }
+  end
+
+  test "show as JSON with include_unread includes read notifications" do
+    notifications = users(:kevin).notifications
+    expected_ids = notifications.unread.ordered.limit(100).pluck(:id) +
+      notifications.read.ordered.limit(100).pluck(:id)
+
+    get tray_notifications_path(format: :json, include_unread: true)
+
+    assert_response :success
+    assert_equal expected_ids, @response.parsed_body.map { |s| s["id"] }
   end
 end