diff --git a/.changesets/padrino-boot-loop.md b/.changesets/padrino-boot-loop.md
new file mode 100644
index 000000000..e3433cc8d
--- /dev/null
+++ b/.changesets/padrino-boot-loop.md
@@ -0,0 +1,7 @@
+---
+bump: patch
+type: fix
+---
+
+Fix issue with AppSignal getting stuck in a boot loop when loading the Padrino integration with: `require "appsignal/integrations/padrino"`
+This could happen in nested applications, like a Padrino app in a Rails app. AppSignal will now use the first config AppSignal starts with.
diff --git a/lib/appsignal/integrations/padrino.rb b/lib/appsignal/integrations/padrino.rb
index 0dce5dc9f..748989ded 100644
--- a/lib/appsignal/integrations/padrino.rb
+++ b/lib/appsignal/integrations/padrino.rb
@@ -13,9 +13,11 @@ def self.init
         Padrino.before_load do
           Appsignal.internal_logger.debug("Loading Padrino (#{Padrino::VERSION}) integration")
 
-          root = Padrino.mounted_root
-          Appsignal.config = Appsignal::Config.new(root, Padrino.env)
-          Appsignal.start
+          unless Appsignal.active?
+            root = Padrino.mounted_root
+            Appsignal.config = Appsignal::Config.new(root, Padrino.env)
+            Appsignal.start
+          end
 
           next unless Appsignal.active?
 
diff --git a/spec/lib/appsignal/integrations/padrino_spec.rb b/spec/lib/appsignal/integrations/padrino_spec.rb
index e04cd18eb..8c7c7a017 100644
--- a/spec/lib/appsignal/integrations/padrino_spec.rb
+++ b/spec/lib/appsignal/integrations/padrino_spec.rb
@@ -24,6 +24,37 @@ def uninstall_padrino_integration
         end
       end
 
+      context "when already active" do
+        before { allow(Appsignal).to receive(:active?).and_return(true) }
+
+        it "does not start AppSignal again" do
+          expect(Appsignal::Config).to_not receive(:new)
+          expect(Appsignal).to_not receive(:start)
+
+          Appsignal::Integrations::PadrinoPlugin.init
+          callbacks[:before_load].call
+        end
+
+        it "adds the instrumentation middleware to Sinatra::Base" do
+          Appsignal::Integrations::PadrinoPlugin.init
+          callbacks[:before_load].call
+
+          middlewares = Padrino.middleware
+          expect(middlewares).to include(
+            [Rack::Events, [[instance_of(Appsignal::Rack::EventHandler)]], nil]
+          )
+          expect(middlewares).to include(
+            [
+              Appsignal::Rack::SinatraBaseInstrumentation,
+              [
+                :instrument_span_name => "process_action.padrino"
+              ],
+              nil
+            ]
+          )
+        end
+      end
+
       context "with active config" do
         before do
           ENV["APPSIGNAL_APP_NAME"] = "My Padrino app name"