diff --git a/app/assets/javascripts/discourse/initializers/live-development.js.es6 b/app/assets/javascripts/discourse/initializers/live-development.js.es6
index c6dba5fdfcf..de482647b35 100644
--- a/app/assets/javascripts/discourse/initializers/live-development.js.es6
+++ b/app/assets/javascripts/discourse/initializers/live-development.js.es6
@@ -7,6 +7,28 @@ export default {
   initialize(container) {
     const messageBus = container.lookup('message-bus:main');
 
+    if (window.history && window.location.search.indexOf("?preview_theme_key=") === 0) {
+      // force preview theme key to always be carried along
+      const themeKey = window.location.search.slice(19).split('&')[0];
+      if (themeKey.match(/^[a-z0-9-]+$/i)) {
+        const patchState = function(f) {
+          const patched = window.history[f];
+
+          window.history[f] = function(stateObj, name, url) {
+            if (url.indexOf("preview_theme_key=") === -1) {
+              const joiner = url.indexOf("?") === -1 ? "?" : "&";
+              url = `${url}${joiner}preview_theme_key=${themeKey}`;
+            }
+
+            return patched.call(window.history, stateObj, name, url);
+          };
+        };
+        patchState("replaceState");
+        patchState("pushState");
+      }
+
+    }
+
     // Custom header changes
     $('header.custom').each(function() {
       const header = $(this);
diff --git a/app/controllers/admin/themes_controller.rb b/app/controllers/admin/themes_controller.rb
index 77fb2009d1c..99b4caa3bd7 100644
--- a/app/controllers/admin/themes_controller.rb
+++ b/app/controllers/admin/themes_controller.rb
@@ -7,8 +7,7 @@ class Admin::ThemesController < Admin::AdminController
 
   def preview
     @theme = Theme.find(params[:id])
-
-    redirect_to path("/"), flash: { preview_theme_key: @theme.key }
+    redirect_to path("/?preview_theme_key=#{@theme.key}")
   end
 
   def upload_asset
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index e02d7343368..f2a7b475012 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -315,7 +315,7 @@ class ApplicationController < ActionController::Base
     resolve_safe_mode
     return if request.env[NO_CUSTOM]
 
-    theme_key = flash[:preview_theme_key]
+    theme_key = request[:preview_theme_key]
 
     user_option = current_user&.user_option