diff --git a/CHANGELOG.md b/CHANGELOG.md
index 92d925c8..1a620069 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@
 
 ### Fixed
 
+- [OpenAPI] Avoid caching a request-specific spec URL in the HTML docs page.
 - [Router] Compose and restore `SCRIPT_NAME` correctly for mounted Rack apps.
 - [OpenAPI] Fix schema registry key collisions for Blueprinter classes referenced under different views.
 
diff --git a/lib/rage/openapi/index.html.erb b/lib/rage/openapi/index.html.erb
index 13b8c4b6..aeb31b87 100644
--- a/lib/rage/openapi/index.html.erb
+++ b/lib/rage/openapi/index.html.erb
@@ -13,7 +13,7 @@
     <script>
       window.onload = () => {
         window.ui = SwaggerUIBundle({
-          url: '<%= spec_url %>',
+          url: window.location.pathname.replace(/\/?$/, "/json"),
           dom_id: '#swagger-ui',
         });
       };
diff --git a/lib/rage/openapi/openapi.rb b/lib/rage/openapi/openapi.rb
index b9abc145..a7c89b99 100644
--- a/lib/rage/openapi/openapi.rb
+++ b/lib/rage/openapi/openapi.rb
@@ -42,11 +42,9 @@ module Rage::OpenAPI
   #     run Rage.openapi.application(namespace: "Api::V2")
   #   end
   def self.application(namespace: nil)
-    html_app = ->(env) do
+    html_app = ->(_) do
       __data_cache[[:page, namespace]] ||= begin
-        scheme, host, path = env["rack.url_scheme"], env["HTTP_HOST"], env["SCRIPT_NAME"]
-        spec_url = "#{scheme}://#{host}#{path}/json"
-        page = ERB.new(File.read("#{__dir__}/index.html.erb")).result(binding)
+        page = ERB.new(File.read("#{__dir__}/index.html.erb")).result
 
         [200, { "content-type" => "text/html; charset=UTF-8" }, [page]]
       end
diff --git a/spec/openapi/openapi_spec.rb b/spec/openapi/openapi_spec.rb
index af331453..e71187fa 100644
--- a/spec/openapi/openapi_spec.rb
+++ b/spec/openapi/openapi_spec.rb
@@ -3,6 +3,42 @@
 require "prism"
 
 RSpec.describe Rage::OpenAPI do
+  describe ".application" do
+    subject(:app) { described_class.application }
+
+    let(:first_env) do
+      {
+        "PATH_INFO" => "/",
+        "SCRIPT_NAME" => "/docs-a",
+        "HTTP_HOST" => "first.test:3000",
+        "rack.url_scheme" => "http"
+      }
+    end
+
+    let(:second_env) do
+      {
+        "PATH_INFO" => "/",
+        "SCRIPT_NAME" => "/docs-b",
+        "HTTP_HOST" => "second.test:4000",
+        "rack.url_scheme" => "https"
+      }
+    end
+
+    before do
+      allow(Rage.config).to receive(:middleware).and_return([])
+    end
+
+    it "renders a request-independent html page" do
+      _, _, first_body = app.call(first_env)
+      _, _, second_body = app.call(second_env)
+
+      expect(first_body.join).to eq(second_body.join)
+      expect(first_body.join).to include('url: window.location.pathname.replace(/\/?$/, "/json"),')
+      expect(first_body.join).not_to include("first.test:3000")
+      expect(first_body.join).not_to include("/docs-a/json")
+    end
+  end
+
   describe ".__try_parse_collection" do
     subject { described_class.__try_parse_collection(input) }