diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index bf9e764b39e..aa29468fb26 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -269,7 +269,8 @@ class ApplicationController < ActionController::Base
       find_opts[:active] = true unless opts[:include_inactive]
       User.find_by(find_opts)
     elsif params[:external_id]
-      SingleSignOnRecord.find_by(external_id: params[:external_id]).try(:user)
+      external_id = params[:external_id].gsub(/\.json$/, '')
+      SingleSignOnRecord.find_by(external_id: external_id).try(:user)
     end
     raise Discourse::NotFound if user.blank?
 
diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
index 3a10834b85c..ad0b3699fcb 100644
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -39,6 +39,12 @@ class UsersController < ApplicationController
       user_serializer.topic_post_count = {topic_id => Post.where(topic_id: topic_id, user_id: @user.id).count }
     end
 
+    # This is a hack to get around a Rails issue where values with periods aren't handled correctly
+    # when used as part of a route.
+    if params[:external_id] and params[:external_id].ends_with? '.json'
+      return render_json_dump(user_serializer)
+    end
+
     respond_to do |format|
       format.html do
         @restrict_fields = guardian.restrict_user_fields?(@user)
diff --git a/config/routes.rb b/config/routes.rb
index 86ceb31d2ed..98b2f9df822 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -275,7 +275,8 @@ Discourse::Application.routes.draw do
   get "users/:username/notifications" => "users#show", constraints: {username: USERNAME_ROUTE_FORMAT}
   get "users/:username/pending" => "users#show", constraints: {username: USERNAME_ROUTE_FORMAT}
   delete "users/:username" => "users#destroy", constraints: {username: USERNAME_ROUTE_FORMAT}
-  get "users/by-external/:external_id" => "users#show"
+  # The external_id constraint is to allow periods to be used in the value without becoming part of the format. ie: foo.bar.json
+  get "users/by-external/:external_id" => "users#show", constraints: {external_id: /[^\/]+/}
   get "users/:username/flagged-posts" => "users#show", constraints: {username: USERNAME_ROUTE_FORMAT}
   get "users/:username/deleted-posts" => "users#show", constraints: {username: USERNAME_ROUTE_FORMAT}
   get "user-badges/:username" => "user_badges#username"