diff --git a/lib/kamal/cli/templates/deploy.yml b/lib/kamal/cli/templates/deploy.yml
index 2602c66d8..119961b9d 100644
--- a/lib/kamal/cli/templates/deploy.yml
+++ b/lib/kamal/cli/templates/deploy.yml
@@ -18,6 +18,10 @@ registry:
   password:
     - KAMAL_REGISTRY_PASSWORD
 
+# Configure builder setup.
+builder:
+  arch: amd64
+
 # Inject ENV variables into containers (secrets come from .env).
 # Remember to run `kamal env push` after making changes!
 # env:
@@ -30,16 +34,6 @@ registry:
 # ssh:
 #   user: app
 
-# Configure builder setup.
-# builder:
-#   args:
-#     RUBY_VERSION: 3.2.0
-#   secrets:
-#     - GITHUB_TOKEN
-#   remote:
-#     arch: amd64
-#     host: ssh://app@192.168.0.1
-
 # Use accessory services (secrets come from .env).
 # accessories:
 #   db:
diff --git a/lib/kamal/configuration/validator/builder.rb b/lib/kamal/configuration/validator/builder.rb
index ebccdf817..4bd815bfd 100644
--- a/lib/kamal/configuration/validator/builder.rb
+++ b/lib/kamal/configuration/validator/builder.rb
@@ -5,5 +5,7 @@ def validate!
     if config["cache"] && config["cache"]["type"]
       error "Invalid cache type: #{config["cache"]["type"]}" unless [ "gha", "registry" ].include?(config["cache"]["type"])
     end
+
+    error "Builder arch not set" unless config["arch"].present?
   end
 end
diff --git a/test/cli/build_test.rb b/test/cli/build_test.rb
index c8f01540a..11b6fb1eb 100644
--- a/test/cli/build_test.rb
+++ b/test/cli/build_test.rb
@@ -26,7 +26,7 @@ class CliBuildTest < CliTestCase
         assert_match /Cloning repo into build directory/, output
         assert_match /git -C #{Dir.tmpdir}\/kamal-clones\/app-#{pwd_sha} clone #{Dir.pwd}/, output
         assert_match /docker --version && docker buildx version/, output
-        assert_match /docker build --push --platform linux\/amd64,linux\/arm64 --builder kamal-local-docker-container -t dhh\/app:999 -t dhh\/app:latest --label service="app" --file Dockerfile \. as .*@localhost/, output
+        assert_match /docker build --push --platform linux\/amd64 --builder kamal-local-docker-container -t dhh\/app:999 -t dhh\/app:latest --label service="app" --file Dockerfile \. as .*@localhost/, output
       end
     end
   end
@@ -49,7 +49,7 @@ class CliBuildTest < CliTestCase
       SSHKit::Backend::Abstract.any_instance.expects(:execute).with(:git, "-C", build_directory, :submodule, :update, "--init")
 
       SSHKit::Backend::Abstract.any_instance.expects(:execute)
-        .with(:docker, :build, "--push", "--platform", "linux/amd64,linux/arm64", "--builder", "kamal-local-docker-container", "-t", "dhh/app:999", "-t", "dhh/app:latest", "--label", "service=\"app\"", "--file", "Dockerfile", ".")
+        .with(:docker, :build, "--push", "--platform", "linux/amd64", "--builder", "kamal-local-docker-container", "-t", "dhh/app:999", "-t", "dhh/app:latest", "--label", "service=\"app\"", "--file", "Dockerfile", ".")
 
       SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
         .with(:git, "-C", anything, :"rev-parse", :HEAD)
@@ -74,7 +74,7 @@ class CliBuildTest < CliTestCase
       assert_no_match /Cloning repo into build directory/, output
       assert_hook_ran "pre-build", output, **hook_variables
       assert_match /docker --version && docker buildx version/, output
-      assert_match /docker build --push --platform linux\/amd64,linux\/arm64 --builder kamal-local-docker-container -t dhh\/app:999 -t dhh\/app:latest --label service="app" --file Dockerfile . as .*@localhost/, output
+      assert_match /docker build --push --platform linux\/amd64 --builder kamal-local-docker-container -t dhh\/app:999 -t dhh\/app:latest --label service="app" --file Dockerfile . as .*@localhost/, output
     end
   end
 
@@ -137,7 +137,7 @@ class CliBuildTest < CliTestCase
         .returns("")
 
       SSHKit::Backend::Abstract.any_instance.expects(:execute)
-        .with(:docker, :build, "--push", "--platform", "linux/amd64,linux/arm64", "--builder", "kamal-local-docker-container", "-t", "dhh/app:999", "-t", "dhh/app:latest", "--label", "service=\"app\"", "--file", "Dockerfile", ".")
+        .with(:docker, :build, "--push", "--platform", "linux/amd64", "--builder", "kamal-local-docker-container", "-t", "dhh/app:999", "-t", "dhh/app:latest", "--label", "service=\"app\"", "--file", "Dockerfile", ".")
 
       run_command("push").tap do |output|
         assert_match /WARN Missing compatible builder, so creating a new one first/, output
diff --git a/test/commands/accessory_test.rb b/test/commands/accessory_test.rb
index 94c1bebcb..400029884 100644
--- a/test/commands/accessory_test.rb
+++ b/test/commands/accessory_test.rb
@@ -5,6 +5,7 @@ class CommandsAccessoryTest < ActiveSupport::TestCase
     @config = {
       service: "app", image: "dhh/app", registry: { "server" => "private.registry", "username" => "dhh", "password" => "secret" },
       servers: [ "1.1.1.1" ],
+      builder: { "arch" => "amd64" },
       accessories: {
         "mysql" => {
           "image" => "private.registry/mysql:8.0",
diff --git a/test/commands/app_test.rb b/test/commands/app_test.rb
index 502501cd7..bee7dc34b 100644
--- a/test/commands/app_test.rb
+++ b/test/commands/app_test.rb
@@ -5,7 +5,7 @@ class CommandsAppTest < ActiveSupport::TestCase
     ENV["RAILS_MASTER_KEY"] = "456"
     Kamal::Configuration.any_instance.stubs(:run_id).returns("12345678901234567890123456789012")
 
-    @config = { service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ], env: { "secret" => [ "RAILS_MASTER_KEY" ] } }
+    @config = { service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ], env: { "secret" => [ "RAILS_MASTER_KEY" ] }, builder: { "arch" => "amd64" } }
   end
 
   teardown do
diff --git a/test/commands/auditor_test.rb b/test/commands/auditor_test.rb
index 5b7a34c55..2aaafd677 100644
--- a/test/commands/auditor_test.rb
+++ b/test/commands/auditor_test.rb
@@ -8,7 +8,7 @@ class CommandsAuditorTest < ActiveSupport::TestCase
     freeze_time
 
     @config = {
-      service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ]
+      service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, builder: { "arch" => "amd64" },  servers: [ "1.1.1.1" ]
     }
 
     @auditor = new_command
diff --git a/test/commands/builder_test.rb b/test/commands/builder_test.rb
index 960c17fe5..b70941268 100644
--- a/test/commands/builder_test.rb
+++ b/test/commands/builder_test.rb
@@ -2,14 +2,14 @@
 
 class CommandsBuilderTest < ActiveSupport::TestCase
   setup do
-    @config = { service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ] }
+    @config = { service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ], builder: { "arch" => "amd64" } }
   end
 
-  test "target linux/amd64,linux/arm64 locally by default" do
+  test "target linux/amd64 locally by default" do
     builder = new_builder_command(builder: { "cache" => { "type" => "gha" } })
     assert_equal "local", builder.name
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
@@ -25,12 +25,12 @@ class CommandsBuilderTest < ActiveSupport::TestCase
     builder = new_builder_command(builder: { "cache" => { "type" => "gha" } })
     assert_equal "local", builder.name
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
-  test "hybrid build if remote is set" do
-    builder = new_builder_command(builder: { "remote" => "ssh://app@127.0.0.1", "cache" => { "type" => "gha" } })
+  test "hybrid build if remote is set and building multiarch" do
+    builder = new_builder_command(builder: { "arch" => [ "amd64", "arm64" ], "remote" => "ssh://app@127.0.0.1", "cache" => { "type" => "gha" } })
     assert_equal "hybrid", builder.name
     assert_equal \
       "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-hybrid-docker-container-ssh---app-127-0-0-1 -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
@@ -93,21 +93,21 @@ class CommandsBuilderTest < ActiveSupport::TestCase
   test "build context" do
     builder = new_builder_command(builder: { "context" => ".." })
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ..",
+      "docker build --push --platform linux/amd64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ..",
       builder.push.join(" ")
   end
 
   test "push with build args" do
     builder = new_builder_command(builder: { "args" => { "a" => 1, "b" => 2 } })
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --build-arg a=\"1\" --build-arg b=\"2\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --build-arg a=\"1\" --build-arg b=\"2\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
   test "push with build secrets" do
     builder = new_builder_command(builder: { "secrets" => [ "a", "b" ] })
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --secret id=\"a\" --secret id=\"b\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --secret id=\"a\" --secret id=\"b\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
@@ -126,7 +126,7 @@ class CommandsBuilderTest < ActiveSupport::TestCase
   test "context build" do
     builder = new_builder_command(builder: { "context" => "./foo" })
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ./foo",
+      "docker build --push --platform linux/amd64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ./foo",
       builder.push.join(" ")
   end
 
@@ -137,7 +137,7 @@ class CommandsBuilderTest < ActiveSupport::TestCase
 
   private
     def new_builder_command(additional_config = {})
-      Kamal::Commands::Builder.new(Kamal::Configuration.new(@config.merge(additional_config), version: "123"))
+      Kamal::Commands::Builder.new(Kamal::Configuration.new(@config.deep_merge(additional_config), version: "123"))
     end
 
     def build_directory
diff --git a/test/commands/docker_test.rb b/test/commands/docker_test.rb
index 0c0e976b9..db2ed45c5 100644
--- a/test/commands/docker_test.rb
+++ b/test/commands/docker_test.rb
@@ -3,7 +3,7 @@
 class CommandsDockerTest < ActiveSupport::TestCase
   setup do
     @config = {
-      service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ]
+      service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ], builder: { "arch" => "amd64" }
     }
     @docker = Kamal::Commands::Docker.new(Kamal::Configuration.new(@config))
   end
diff --git a/test/commands/hook_test.rb b/test/commands/hook_test.rb
index c0e6e98fa..60438c66f 100644
--- a/test/commands/hook_test.rb
+++ b/test/commands/hook_test.rb
@@ -8,7 +8,7 @@ class CommandsHookTest < ActiveSupport::TestCase
 
     @config = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ],
-      traefik: { "args" => { "accesslog.format" => "json", "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
+      builder: { "arch" => "amd64" }, traefik: { "args" => { "accesslog.format" => "json", "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
     }
 
     @performer = Kamal::Git.email.presence || `whoami`.chomp
diff --git a/test/commands/lock_test.rb b/test/commands/lock_test.rb
index fc2b15abb..028719220 100644
--- a/test/commands/lock_test.rb
+++ b/test/commands/lock_test.rb
@@ -4,7 +4,7 @@ class CommandsLockTest < ActiveSupport::TestCase
   setup do
     @config = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ],
-      traefik: { "args" => { "accesslog.format" => "json", "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
+      builder: { "arch" => "amd64" }, traefik: { "args" => { "accesslog.format" => "json", "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
     }
   end
 
diff --git a/test/commands/prune_test.rb b/test/commands/prune_test.rb
index c4a56a9a2..430a13db6 100644
--- a/test/commands/prune_test.rb
+++ b/test/commands/prune_test.rb
@@ -4,7 +4,7 @@ class CommandsPruneTest < ActiveSupport::TestCase
   setup do
     @config = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ],
-      traefik: { "args" => { "accesslog.format" => "json", "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
+      builder: { "arch" => "amd64" }, traefik: { "args" => { "accesslog.format" => "json", "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
     }
   end
 
diff --git a/test/commands/registry_test.rb b/test/commands/registry_test.rb
index c25d75853..17376fef9 100755
--- a/test/commands/registry_test.rb
+++ b/test/commands/registry_test.rb
@@ -8,6 +8,7 @@ class CommandsRegistryTest < ActiveSupport::TestCase
         "password" => "secret",
         "server" => "hub.docker.com"
       },
+      builder: { "arch" => "amd64" },
       servers: [ "1.1.1.1" ]
     }
     @registry = Kamal::Commands::Registry.new Kamal::Configuration.new(@config)
diff --git a/test/commands/server_test.rb b/test/commands/server_test.rb
index 9e063f77d..8c465fd9d 100644
--- a/test/commands/server_test.rb
+++ b/test/commands/server_test.rb
@@ -4,7 +4,7 @@ class CommandsServerTest < ActiveSupport::TestCase
   setup do
     @config = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ],
-      traefik: { "args" => { "accesslog.format" => "json", "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
+      builder: { "arch" => "amd64" }, traefik: { "args" => { "accesslog.format" => "json", "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
     }
   end
 
diff --git a/test/commands/traefik_test.rb b/test/commands/traefik_test.rb
index a46fc2845..446c3077e 100644
--- a/test/commands/traefik_test.rb
+++ b/test/commands/traefik_test.rb
@@ -5,7 +5,7 @@ class CommandsTraefikTest < ActiveSupport::TestCase
     @image = "traefik:test"
 
     @config = {
-      service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ],
+      service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ], builder: { "arch" => "amd64" },
       traefik: { "image" => @image, "args" => { "accesslog.format" => "json", "api.insecure" => true, "metrics.prometheus.buckets" => "0.1,0.3,1.2,5.0" } }
     }
 
diff --git a/test/configuration/accessory_test.rb b/test/configuration/accessory_test.rb
index 581cdab34..3f939607d 100644
--- a/test/configuration/accessory_test.rb
+++ b/test/configuration/accessory_test.rb
@@ -8,6 +8,7 @@ class ConfigurationAccessoryTest < ActiveSupport::TestCase
         "web" => [ "1.1.1.1", "1.1.1.2" ],
         "workers" => [ "1.1.1.3", "1.1.1.4" ]
       },
+      builder: { "arch" => "amd64" },
       env: { "REDIS_URL" => "redis://x/y" },
       accessories: {
         "mysql" => {
diff --git a/test/configuration/builder_test.rb b/test/configuration/builder_test.rb
index efcd613b5..3df477c95 100644
--- a/test/configuration/builder_test.rb
+++ b/test/configuration/builder_test.rb
@@ -4,13 +4,7 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   setup do
     @deploy = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" },
-      servers: [ "1.1.1.1" ]
-    }
-
-    @deploy_with_builder_option = {
-      service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" },
-      servers: [ "1.1.1.1" ],
-      builder: {}
+      builder: { "arch" => "amd64" }, servers: [ "1.1.1.1" ]
     }
   end
 
@@ -27,16 +21,16 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   end
 
   test "setting both local and remote configs" do
-    @deploy_with_builder_option[:builder] = {
+    @deploy[:builder] = {
       "arch" => [ "amd64", "arm64" ],
       "remote" => "ssh://root@192.168.0.1"
     }
 
-    assert_equal true, config_with_builder_option.builder.local?
-    assert_equal true, config_with_builder_option.builder.remote?
+    assert_equal true, config.builder.local?
+    assert_equal true, config.builder.remote?
 
-    assert_equal [ "amd64", "arm64" ], config_with_builder_option.builder.arches
-    assert_equal "ssh://root@192.168.0.1", config_with_builder_option.builder.remote
+    assert_equal [ "amd64", "arm64" ], config.builder.arches
+    assert_equal "ssh://root@192.168.0.1", config.builder.remote
   end
 
   test "cached?" do
@@ -44,10 +38,10 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   end
 
   test "invalid cache type specified" do
-    @deploy_with_builder_option[:builder] = { "cache" => { "type" => "invalid" } }
+    @deploy[:builder]["cache"] = { "type" => "invalid" }
 
     assert_raises(Kamal::ConfigurationError) do
-      config_with_builder_option.builder
+      config.builder
     end
   end
 
@@ -60,32 +54,32 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   end
 
   test "setting gha cache" do
-    @deploy_with_builder_option[:builder] = { "cache" => { "type" => "gha", "options" => "mode=max" } }
+    @deploy[:builder] = { "arch" => "amd64", "cache" => { "type" => "gha", "options" => "mode=max" } }
 
-    assert_equal "type=gha", config_with_builder_option.builder.cache_from
-    assert_equal "type=gha,mode=max", config_with_builder_option.builder.cache_to
+    assert_equal "type=gha", config.builder.cache_from
+    assert_equal "type=gha,mode=max", config.builder.cache_to
   end
 
   test "setting registry cache" do
-    @deploy_with_builder_option[:builder] = { "cache" => { "type" => "registry", "options" => "mode=max,image-manifest=true,oci-mediatypes=true" } }
+    @deploy[:builder] = { "arch" => "amd64", "cache" => { "type" => "registry", "options" => "mode=max,image-manifest=true,oci-mediatypes=true" } }
 
-    assert_equal "type=registry,ref=dhh/app-build-cache", config_with_builder_option.builder.cache_from
-    assert_equal "type=registry,mode=max,image-manifest=true,oci-mediatypes=true,ref=dhh/app-build-cache", config_with_builder_option.builder.cache_to
+    assert_equal "type=registry,ref=dhh/app-build-cache", config.builder.cache_from
+    assert_equal "type=registry,mode=max,image-manifest=true,oci-mediatypes=true,ref=dhh/app-build-cache", config.builder.cache_to
   end
 
   test "setting registry cache when using a custom registry" do
-    @deploy_with_builder_option[:registry]["server"] = "registry.example.com"
-    @deploy_with_builder_option[:builder] = { "cache" => { "type" => "registry", "options" => "mode=max,image-manifest=true,oci-mediatypes=true" } }
+    @deploy[:registry]["server"] = "registry.example.com"
+    @deploy[:builder] = { "arch" => "amd64", "cache" => { "type" => "registry", "options" => "mode=max,image-manifest=true,oci-mediatypes=true" } }
 
-    assert_equal "type=registry,ref=registry.example.com/dhh/app-build-cache", config_with_builder_option.builder.cache_from
-    assert_equal "type=registry,mode=max,image-manifest=true,oci-mediatypes=true,ref=registry.example.com/dhh/app-build-cache", config_with_builder_option.builder.cache_to
+    assert_equal "type=registry,ref=registry.example.com/dhh/app-build-cache", config.builder.cache_from
+    assert_equal "type=registry,mode=max,image-manifest=true,oci-mediatypes=true,ref=registry.example.com/dhh/app-build-cache", config.builder.cache_to
   end
 
   test "setting registry cache with image" do
-    @deploy_with_builder_option[:builder] = { "cache" => { "type" => "registry", "image" => "kamal", "options" => "mode=max" } }
+    @deploy[:builder] = { "arch" => "amd64", "cache" => { "type" => "registry", "image" => "kamal", "options" => "mode=max" } }
 
-    assert_equal "type=registry,ref=kamal", config_with_builder_option.builder.cache_from
-    assert_equal "type=registry,mode=max,ref=kamal", config_with_builder_option.builder.cache_to
+    assert_equal "type=registry,ref=kamal", config.builder.cache_from
+    assert_equal "type=registry,mode=max,ref=kamal", config.builder.cache_to
   end
 
   test "args" do
@@ -93,9 +87,9 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   end
 
   test "setting args" do
-    @deploy_with_builder_option[:builder] = { "args" => { "key" => "value" } }
+    @deploy[:builder]["args"] = { "key" => "value" }
 
-    assert_equal({ "key" => "value" }, config_with_builder_option.builder.args)
+    assert_equal({ "key" => "value" }, config.builder.args)
   end
 
   test "secrets" do
@@ -103,9 +97,9 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   end
 
   test "setting secrets" do
-    @deploy_with_builder_option[:builder] = { "secrets" => [ "GITHUB_TOKEN" ] }
+    @deploy[:builder]["secrets"] = [ "GITHUB_TOKEN" ]
 
-    assert_equal [ "GITHUB_TOKEN" ], config_with_builder_option.builder.secrets
+    assert_equal [ "GITHUB_TOKEN" ], config.builder.secrets
   end
 
   test "dockerfile" do
@@ -113,9 +107,9 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   end
 
   test "setting dockerfile" do
-    @deploy_with_builder_option[:builder] = { "dockerfile" => "Dockerfile.dev" }
+    @deploy[:builder]["dockerfile"] = "Dockerfile.dev"
 
-    assert_equal "Dockerfile.dev", config_with_builder_option.builder.dockerfile
+    assert_equal "Dockerfile.dev", config.builder.dockerfile
   end
 
   test "context" do
@@ -123,9 +117,9 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   end
 
   test "setting context" do
-    @deploy_with_builder_option[:builder] = { "context" => ".." }
+    @deploy[:builder]["context"] = ".."
 
-    assert_equal "..", config_with_builder_option.builder.context
+    assert_equal "..", config.builder.context
   end
 
   test "ssh" do
@@ -133,17 +127,13 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
   end
 
   test "setting ssh params" do
-    @deploy_with_builder_option[:builder] = { "ssh" => "default=$SSH_AUTH_SOCK" }
+    @deploy[:builder]["ssh"] = "default=$SSH_AUTH_SOCK"
 
-    assert_equal "default=$SSH_AUTH_SOCK", config_with_builder_option.builder.ssh
+    assert_equal "default=$SSH_AUTH_SOCK", config.builder.ssh
   end
 
   private
     def config
       Kamal::Configuration.new(@deploy)
     end
-
-    def config_with_builder_option
-      Kamal::Configuration.new(@deploy_with_builder_option)
-    end
 end
diff --git a/test/configuration/env/tags_test.rb b/test/configuration/env/tags_test.rb
index c36b6057b..0fb649d1d 100644
--- a/test/configuration/env/tags_test.rb
+++ b/test/configuration/env/tags_test.rb
@@ -5,6 +5,7 @@ class ConfigurationEnvTagsTest < ActiveSupport::TestCase
     @deploy = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" },
       servers: [ { "1.1.1.1" => "odd" }, { "1.1.1.2" => "even" }, { "1.1.1.3" => [ "odd", "three" ] } ],
+      builder: { "arch" => "amd64" },
       env: {
         "clear" => { "REDIS_URL" => "redis://x/y", "THREE" => "false" },
         "tags" => {
@@ -64,6 +65,7 @@ class ConfigurationEnvTagsTest < ActiveSupport::TestCase
     deploy = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" },
       servers: [ { "1.1.1.1" => [ "first", "second" ] } ],
+      builder: { "arch" => "amd64" },
       env: {
         "tags" => {
           "first" => { "TYPE" => "first" },
@@ -82,6 +84,7 @@ class ConfigurationEnvTagsTest < ActiveSupport::TestCase
     deploy = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" },
       servers: [ { "1.1.1.1" => "secrets" } ],
+      builder: { "arch" => "amd64" },
       env: {
         "tags" => {
           "secrets" => { "secret" => [ "PASSWORD" ] }
@@ -99,6 +102,7 @@ class ConfigurationEnvTagsTest < ActiveSupport::TestCase
     deploy = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" },
       servers: [ { "1.1.1.1" => "clearly" } ],
+      builder: { "arch" => "amd64" },
       env: {
         "tags" => {
           "clearly" => { "clear" => { "FOO" => "bar" } }
diff --git a/test/configuration/role_test.rb b/test/configuration/role_test.rb
index da9a3d1c5..37c26fcdf 100644
--- a/test/configuration/role_test.rb
+++ b/test/configuration/role_test.rb
@@ -5,6 +5,7 @@ class ConfigurationRoleTest < ActiveSupport::TestCase
     @deploy = {
       service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" },
       servers: [ "1.1.1.1", "1.1.1.2" ],
+      builder: { "arch" => "amd64" },
       env: { "REDIS_URL" => "redis://x/y" }
     }
 
diff --git a/test/configuration/ssh_test.rb b/test/configuration/ssh_test.rb
index f49c00559..76d1ae9a7 100644
--- a/test/configuration/ssh_test.rb
+++ b/test/configuration/ssh_test.rb
@@ -5,6 +5,7 @@ class ConfigurationSshTest < ActiveSupport::TestCase
     @deploy = {
       service: "app", image: "dhh/app",
       registry: { "username" => "dhh", "password" => "secret" },
+      builder: { "arch" => "amd64" },
       env: { "REDIS_URL" => "redis://x/y" },
       servers: [ "1.1.1.1", "1.1.1.2" ],
       volumes: [ "/local/path:/container/path" ]
diff --git a/test/configuration/sshkit_test.rb b/test/configuration/sshkit_test.rb
index dc8c22580..1608e6eee 100644
--- a/test/configuration/sshkit_test.rb
+++ b/test/configuration/sshkit_test.rb
@@ -6,6 +6,7 @@ class ConfigurationSshkitTest < ActiveSupport::TestCase
       service: "app", image: "dhh/app",
       registry: { "username" => "dhh", "password" => "secret" },
       env: { "REDIS_URL" => "redis://x/y" },
+      builder: { "arch" => "amd64" },
       servers: [ "1.1.1.1", "1.1.1.2" ],
       volumes: [ "/local/path:/container/path" ]
     }
diff --git a/test/configuration/validation_test.rb b/test/configuration/validation_test.rb
index b39dbc369..ac409e845 100644
--- a/test/configuration/validation_test.rb
+++ b/test/configuration/validation_test.rb
@@ -101,6 +101,7 @@ def assert_error(message, **invalid_config)
       valid_config = {
         service: "app",
         image: "app",
+        builder: { "arch" => "amd64" },
         registry: { "username" => "user", "password" => "secret" },
         servers: [ "1.1.1.1" ]
       }
diff --git a/test/configuration_test.rb b/test/configuration_test.rb
index 043a4c8cb..aa78dda98 100644
--- a/test/configuration_test.rb
+++ b/test/configuration_test.rb
@@ -8,6 +8,7 @@ class ConfigurationTest < ActiveSupport::TestCase
     @deploy = {
       service: "app", image: "dhh/app",
       registry: { "username" => "dhh", "password" => "secret" },
+      builder: { "arch" => "amd64" },
       env: { "REDIS_URL" => "redis://x/y" },
       servers: [ "1.1.1.1", "1.1.1.2" ],
       volumes: [ "/local/path:/container/path" ]
@@ -121,7 +122,7 @@ class ConfigurationTest < ActiveSupport::TestCase
   test "version from uncommitted context" do
     ENV.delete("VERSION")
 
-    config = Kamal::Configuration.new(@deploy.tap { |c| c[:builder] = { "context" => "." } })
+    config = Kamal::Configuration.new(@deploy.tap { |c| c[:builder]["context"] = "." })
 
     Kamal::Git.expects(:revision).returns("git-version")
     Kamal::Git.expects(:uncommitted_changes).returns("M   file\n")
@@ -267,7 +268,7 @@ class ConfigurationTest < ActiveSupport::TestCase
         ssh_options: { user: "root", port: 22, log_level: :fatal, keepalive: true, keepalive_interval: 30 },
         sshkit: {},
         volume_args: [ "--volume", "/local/path:/container/path" ],
-        builder: {},
+        builder: { "arch" => "amd64" },
         logging: [ "--log-opt", "max-size=\"10m\"" ],
         healthcheck: { "cmd"=>"curl -f http://localhost:3000/up || exit 1", "interval" => "1s", "path"=>"/up", "port"=>3000, "max_attempts" => 7, "cord" => "/tmp/kamal-cord", "log_lines" => 50 } }
 
diff --git a/test/fixtures/deploy.erb.yml b/test/fixtures/deploy.erb.yml
index a668fb3a6..9b9d202d0 100644
--- a/test/fixtures/deploy.erb.yml
+++ b/test/fixtures/deploy.erb.yml
@@ -9,3 +9,5 @@ registry:
   server: registry.digitalocean.com
   username: <%= "my-user" %>
   password: <%= "my-password" %>
+builder:
+  arch: amd64
diff --git a/test/fixtures/deploy_for_dest.yml b/test/fixtures/deploy_for_dest.yml
index 96740aecf..1784d95f9 100644
--- a/test/fixtures/deploy_for_dest.yml
+++ b/test/fixtures/deploy_for_dest.yml
@@ -4,3 +4,5 @@ registry:
   server: registry.digitalocean.com
   username: <%= "my-user" %>
   password: <%= "my-password" %>
+builder:
+  arch: amd64
diff --git a/test/fixtures/deploy_for_required_dest.yml b/test/fixtures/deploy_for_required_dest.yml
index 284383636..1102df953 100644
--- a/test/fixtures/deploy_for_required_dest.yml
+++ b/test/fixtures/deploy_for_required_dest.yml
@@ -4,4 +4,6 @@ registry:
   server: registry.digitalocean.com
   username: <%= "my-user" %>
   password: <%= "my-password" %>
+builder:
+  arch: amd64
 require_destination: true
diff --git a/test/fixtures/deploy_primary_web_role_override.yml b/test/fixtures/deploy_primary_web_role_override.yml
index 694a9be7e..aa52f5edd 100644
--- a/test/fixtures/deploy_primary_web_role_override.yml
+++ b/test/fixtures/deploy_primary_web_role_override.yml
@@ -17,4 +17,6 @@ registry:
   server: registry.digitalocean.com
   username: user
   password: pw
+builder:
+  arch: amd64
 primary_role: web_tokyo
diff --git a/test/fixtures/deploy_simple.yml b/test/fixtures/deploy_simple.yml
index 520c138e9..c143f800d 100644
--- a/test/fixtures/deploy_simple.yml
+++ b/test/fixtures/deploy_simple.yml
@@ -6,3 +6,5 @@ servers:
 registry:
   username: user
   password: pw
+builder:
+  arch: amd64
diff --git a/test/fixtures/deploy_with_accessories.yml b/test/fixtures/deploy_with_accessories.yml
index dd78e9f47..29f502ece 100644
--- a/test/fixtures/deploy_with_accessories.yml
+++ b/test/fixtures/deploy_with_accessories.yml
@@ -10,6 +10,8 @@ servers:
 registry:
   username: user
   password: pw
+builder:
+  arch: amd64
 
 accessories:
   mysql:
diff --git a/test/fixtures/deploy_with_assets.yml b/test/fixtures/deploy_with_assets.yml
index 0b6b7cf52..2879d445c 100644
--- a/test/fixtures/deploy_with_assets.yml
+++ b/test/fixtures/deploy_with_assets.yml
@@ -6,4 +6,6 @@ servers:
 registry:
   username: user
   password: pw
+builder:
+  arch: amd64
 asset_path: /public/assets
diff --git a/test/fixtures/deploy_with_boot_strategy.yml b/test/fixtures/deploy_with_boot_strategy.yml
index 7691eb2e1..963bb7c34 100644
--- a/test/fixtures/deploy_with_boot_strategy.yml
+++ b/test/fixtures/deploy_with_boot_strategy.yml
@@ -7,6 +7,8 @@ servers:
   workers:
     - "1.1.1.3"
     - "1.1.1.4"
+builder:
+  arch: amd64
 
 registry:
   username: user
diff --git a/test/fixtures/deploy_with_env_tags.yml b/test/fixtures/deploy_with_env_tags.yml
index f0a247603..6822b49d8 100644
--- a/test/fixtures/deploy_with_env_tags.yml
+++ b/test/fixtures/deploy_with_env_tags.yml
@@ -11,6 +11,8 @@ servers:
     - 1.1.1.4: site1
     - 1.2.1.3: site2
     - 1.2.1.4: [ site2 experimental ]
+builder:
+  arch: amd64
 env:
   clear:
     TEST: "root"
diff --git a/test/fixtures/deploy_with_extensions.yml b/test/fixtures/deploy_with_extensions.yml
index 7d6a9db27..4a5f934a5 100644
--- a/test/fixtures/deploy_with_extensions.yml
+++ b/test/fixtures/deploy_with_extensions.yml
@@ -21,4 +21,6 @@ registry:
   server: registry.digitalocean.com
   username: user
   password: pw
+builder:
+  arch: amd64
 primary_role: web_tokyo
diff --git a/test/fixtures/deploy_with_low_percentage_boot_strategy.yml b/test/fixtures/deploy_with_low_percentage_boot_strategy.yml
index 9b6a3c647..8698b89fe 100644
--- a/test/fixtures/deploy_with_low_percentage_boot_strategy.yml
+++ b/test/fixtures/deploy_with_low_percentage_boot_strategy.yml
@@ -7,6 +7,8 @@ servers:
   workers:
     - "1.1.1.3"
     - "1.1.1.4"
+builder:
+  arch: amd64
 
 registry:
   username: user
diff --git a/test/fixtures/deploy_with_multiple_traefik_roles.yml b/test/fixtures/deploy_with_multiple_traefik_roles.yml
index a36a409f1..a12705831 100644
--- a/test/fixtures/deploy_with_multiple_traefik_roles.yml
+++ b/test/fixtures/deploy_with_multiple_traefik_roles.yml
@@ -26,6 +26,8 @@ servers:
     hosts:
       - 1.1.1.3
       - 1.1.1.4
+builder:
+  arch: amd64
 env:
   REDIS_URL: redis://x/y
 registry:
diff --git a/test/fixtures/deploy_with_percentage_boot_strategy.yml b/test/fixtures/deploy_with_percentage_boot_strategy.yml
index 9b6a3c647..8698b89fe 100644
--- a/test/fixtures/deploy_with_percentage_boot_strategy.yml
+++ b/test/fixtures/deploy_with_percentage_boot_strategy.yml
@@ -7,6 +7,8 @@ servers:
   workers:
     - "1.1.1.3"
     - "1.1.1.4"
+builder:
+  arch: amd64
 
 registry:
   username: user
diff --git a/test/fixtures/deploy_with_remote_builder.yml b/test/fixtures/deploy_with_remote_builder.yml
index a67963c2a..118142f74 100644
--- a/test/fixtures/deploy_with_remote_builder.yml
+++ b/test/fixtures/deploy_with_remote_builder.yml
@@ -32,6 +32,8 @@ accessories:
     port: 6379
     directories:
       - data:/data
+builder:
+  arch: amd64
 
 readiness_delay: 0
 
diff --git a/test/fixtures/deploy_with_remote_builder_and_custom_ports.yml b/test/fixtures/deploy_with_remote_builder_and_custom_ports.yml
index d76100ff6..0f409da4a 100644
--- a/test/fixtures/deploy_with_remote_builder_and_custom_ports.yml
+++ b/test/fixtures/deploy_with_remote_builder_and_custom_ports.yml
@@ -32,6 +32,8 @@ accessories:
     port: 6379
     directories:
       - data:/data
+builder:
+  arch: amd64
 
 readiness_delay: 0
 
diff --git a/test/fixtures/deploy_with_roles.yml b/test/fixtures/deploy_with_roles.yml
index 0e405241d..1eb8cc5c0 100644
--- a/test/fixtures/deploy_with_roles.yml
+++ b/test/fixtures/deploy_with_roles.yml
@@ -14,3 +14,5 @@ registry:
   server: registry.digitalocean.com
   username: user
   password: pw
+builder:
+  arch: amd64
diff --git a/test/fixtures/deploy_with_secrets.yml b/test/fixtures/deploy_with_secrets.yml
index a03cecbf8..35145a3e2 100644
--- a/test/fixtures/deploy_with_secrets.yml
+++ b/test/fixtures/deploy_with_secrets.yml
@@ -9,3 +9,5 @@ registry:
 env:
   secret:
     - PASSWORD
+builder:
+  arch: amd64
diff --git a/test/fixtures/deploy_with_two_roles_one_host.yml b/test/fixtures/deploy_with_two_roles_one_host.yml
index cae054698..939ff7e5e 100644
--- a/test/fixtures/deploy_with_two_roles_one_host.yml
+++ b/test/fixtures/deploy_with_two_roles_one_host.yml
@@ -13,3 +13,5 @@ registry:
   server: registry.digitalocean.com
   username: user
   password: pw
+builder:
+  arch: amd64
diff --git a/test/fixtures/deploy_with_uncommon_hostnames.yml b/test/fixtures/deploy_with_uncommon_hostnames.yml
index 71e7a6018..112f7b394 100644
--- a/test/fixtures/deploy_with_uncommon_hostnames.yml
+++ b/test/fixtures/deploy_with_uncommon_hostnames.yml
@@ -6,3 +6,5 @@ servers:
 registry:
   username: user
   password: pw
+builder:
+  arch: amd64
diff --git a/test/fixtures/deploy_without_clone.yml b/test/fixtures/deploy_without_clone.yml
index abb1224a1..c322155fb 100644
--- a/test/fixtures/deploy_without_clone.yml
+++ b/test/fixtures/deploy_without_clone.yml
@@ -36,4 +36,5 @@ accessories:
 readiness_delay: 0
 
 builder:
+  arch: amd64
   context: "."
diff --git a/test/fixtures/deploy_workers_only.yml b/test/fixtures/deploy_workers_only.yml
index 75cbbde1a..d83adeeb7 100644
--- a/test/fixtures/deploy_workers_only.yml
+++ b/test/fixtures/deploy_workers_only.yml
@@ -10,3 +10,5 @@ primary_role: workers
 registry:
   username: user
   password: pw
+builder:
+  arch: amd64