diff --git a/CHANGELOG.md b/CHANGELOG.md
index 81317c92..485a00e6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,7 @@ and this project adheres to [Break Versioning](https://www.taoensso.com/break-ve
 ### Fixed
 
 - Don't overwrite libpq ENV vars with empty strings (@StantonMatt in #414).
+- Skip generating duplicate routes when running `generate action`. (@sandbergja in #417)
 
 ### Security
 
diff --git a/lib/hanami/cli/files.rb b/lib/hanami/cli/files.rb
index 14061809..d3a77236 100644
--- a/lib/hanami/cli/files.rb
+++ b/lib/hanami/cli/files.rb
@@ -60,6 +60,13 @@ def touch(path)
         created(path)
       end
 
+      def block_contains?(path, target, contents)
+        content = adapter.read(path)
+        class_start = content.index(target)
+        class_end = content.index(/(?:^|\s)#{CLOSE_BLOCK}(?:$|\s)/, class_start)
+        content[class_start..class_end].include? contents
+      end
+
       private
 
       attr_reader :out
diff --git a/lib/hanami/cli/generators/app/action.rb b/lib/hanami/cli/generators/app/action.rb
index e448213e..41d635da 100644
--- a/lib/hanami/cli/generators/app/action.rb
+++ b/lib/hanami/cli/generators/app/action.rb
@@ -85,15 +85,14 @@ def insert_route(key:, namespace:, url_path:, http_method:)
             route = route_definition(key:, url_path:, http_method:)
 
             if namespace == Hanami.app.namespace
-              fs.inject_line_at_class_bottom(routes_location, "class Routes", route)
+              add_route_to_file(file: routes_location, route:)
             else
               slice_routes = fs.join("slices", namespace, "config", "routes.rb")
 
               if fs.exist?(slice_routes)
-                fs.inject_line_at_class_bottom(slice_routes, "class Routes", route)
+                add_route_to_file(file: slice_routes, route:)
               else
-                slice_matcher = /slice[[:space:]]*:#{namespace}/
-                fs.inject_line_at_block_bottom(routes_location, slice_matcher, route)
+                add_route_to_block(file: routes_location, namespace:, route:)
               end
             end
           end
@@ -190,6 +189,24 @@ def route_http(action, http_method)
 
             result
           end
+
+          def add_route_to_file(file:, route:)
+            target_class = "class Routes"
+            if fs.block_contains?(file, target_class, route)
+              out.puts "Route (#{route}) already exists, skipping..."
+            else
+              fs.inject_line_at_class_bottom(file, "class Routes", route)
+            end
+          end
+
+          def add_route_to_block(file:, namespace:, route:)
+            slice_matcher = /slice[[:space:]]*:#{namespace}/
+            if fs.block_contains?(file, slice_matcher, route)
+              out.puts "Route (#{route}) already exists, skipping..."
+            else
+              fs.inject_line_at_block_bottom(file, slice_matcher, route)
+            end
+          end
         end
       end
     end
diff --git a/spec/unit/hanami/cli/commands/app/generate/action_spec.rb b/spec/unit/hanami/cli/commands/app/generate/action_spec.rb
index 5f315f42..5afbe216 100644
--- a/spec/unit/hanami/cli/commands/app/generate/action_spec.rb
+++ b/spec/unit/hanami/cli/commands/app/generate/action_spec.rb
@@ -40,6 +40,31 @@ def error_output = err.string.chomp
       end
     end
 
+    context "when route already exists in route file" do
+      it "does not add a duplicate route" do
+        within_application_directory do
+          routes_contents = <<~CODE
+            # frozen_string_literal: true
+
+            require "hanami/routes"
+
+            module #{app}
+              class Routes < Hanami::Routes
+                root { "Hello from Hanami" }
+                get "/users", to: "users.index"
+              end
+            end
+          CODE
+          fs.write("config/routes.rb", routes_contents)
+
+          generate_action
+
+          expect(fs.read("config/routes.rb")).to eq routes_contents
+          expect(output).to include 'Route (get "/users", to: "users.index") already exists, skipping...'
+        end
+      end
+    end
+
     context "with existing action file" do
       let(:file_path) { "app/actions/#{namespace}/#{action}.rb" }
 
@@ -1252,6 +1277,35 @@ class Routes < Hanami::Routes
         end
       end
 
+      it "does not add a duplicate route to the slice block" do
+        within_application_directory do
+          prepare_slice!
+          fs.mkdir("slices/api")
+
+          routes_contents = <<~CODE
+            # frozen_string_literal: true
+
+            require "hanami/routes"
+
+            module #{app}
+              class Routes < Hanami::Routes
+                root { "Hello from Hanami" }
+
+                slice :#{slice}, at: "/#{slice}" do
+                  get "/home", to: "home.index"
+                end
+              end
+            end
+          CODE
+          fs.write("config/routes.rb", routes_contents)
+
+          subject.call(slice:, name: "home.index")
+
+          expect(fs.read("config/routes.rb")).to eq routes_contents
+          expect(output).to include 'Route (get "/home", to: "home.index") already exists, skipping...'
+        end
+      end
+
       it "raises error if slice is nonexistent" do
         expect {
           subject.call(slice: "foo", name: action_name)