diff --git a/.changesets/don-t-start-for-hanami-if-already-started.md b/.changesets/don-t-start-for-hanami-if-already-started.md
new file mode 100644
index 000000000..b935222ae
--- /dev/null
+++ b/.changesets/don-t-start-for-hanami-if-already-started.md
@@ -0,0 +1,7 @@
+---
+bump: patch
+type: fix
+---
+
+Fix issue with AppSignal getting stuck in a boot loop when loading the Hanami integration with: `require "appsignal/integrations/hanami"`
+This could happen in nested applications, like a Hanami app in a Rails app. It will now use the first config AppSignal starts with.
diff --git a/lib/appsignal/integrations/hanami.rb b/lib/appsignal/integrations/hanami.rb
index 97e99f8e8..31b3d468c 100644
--- a/lib/appsignal/integrations/hanami.rb
+++ b/lib/appsignal/integrations/hanami.rb
@@ -11,12 +11,14 @@ def self.init
         Appsignal.internal_logger.debug("Loading Hanami integration")
 
         hanami_app_config = ::Hanami.app.config
-        Appsignal.config = Appsignal::Config.new(
-          hanami_app_config.root || Dir.pwd,
-          hanami_app_config.env
-        )
 
-        Appsignal.start
+        unless Appsignal.active?
+          Appsignal.config = Appsignal::Config.new(
+            hanami_app_config.root || Dir.pwd,
+            hanami_app_config.env
+          )
+          Appsignal.start
+        end
 
         return unless Appsignal.active?
 
diff --git a/spec/lib/appsignal/integrations/hanami_spec.rb b/spec/lib/appsignal/integrations/hanami_spec.rb
index 1f64c4403..a988ccf1d 100644
--- a/spec/lib/appsignal/integrations/hanami_spec.rb
+++ b/spec/lib/appsignal/integrations/hanami_spec.rb
@@ -74,6 +74,35 @@ def uninstall_hanami_middleware
         end
       end
 
+      context "when AppSignal is already active" do
+        before do
+          expect(Appsignal).to receive(:active?).at_least(1).and_return(true)
+        end
+
+        it "does not initialize AppSignal again" do
+          expect(Appsignal).to_not receive(:start)
+
+          Appsignal::Integrations::HanamiPlugin.init
+        end
+
+        it "prepends the integration to Hanami::Action" do
+          Appsignal::Integrations::HanamiPlugin.init
+
+          expect(::Hanami::Action)
+            .to have_received(:prepend).with(Appsignal::Integrations::HanamiIntegration)
+        end
+
+        it "adds middleware to the Hanami app" do
+          Appsignal::Integrations::HanamiPlugin.init
+
+          expect(::Hanami.app.config.middleware.stack[::Hanami::Router::DEFAULT_PREFIX])
+            .to include(
+              [Rack::Events, [[kind_of(Appsignal::Rack::EventHandler)]], *hanami_middleware_options],
+              [Appsignal::Rack::HanamiMiddleware, [], *hanami_middleware_options]
+            )
+        end
+      end
+
       context "when APPSIGNAL_APP_ENV ENV var is provided" do
         it "uses this as the environment" do
           ENV["APPSIGNAL_APP_ENV"] = "custom"