diff --git a/CHANGELOG.md b/CHANGELOG.md
index 127bab169..eb6fda94d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 Note: For changes to the API, see https://shopify.dev/changelog?filter=api
 ## Unreleased
+- Preserve in-place changes to nested REST attributes when saving resources.
 
 ## 16.3.1 (2026-10-22)
 - [#1472](https://github.com/Shopify/shopify-api-ruby/pull/1472) `ShopifyAPI::Auth.embedded_app_url` now raises `ShopifyAPI::Errors::InvalidShopError` unless the decoded `host` is a trusted Shopify Admin host (see `ShopifyAPI::Utils::ShopValidator`). URLs for supported Admin hosts are unchanged.
diff --git a/lib/shopify_api/rest/base.rb b/lib/shopify_api/rest/base.rb
index 3cc4ebd18..c69961039 100644
--- a/lib/shopify_api/rest/base.rb
+++ b/lib/shopify_api/rest/base.rb
@@ -3,6 +3,7 @@
 
 require "active_support/inflector"
 require "active_support/core_ext/hash/indifferent_access"
+require "active_support/core_ext/object/deep_dup"
 
 module ShopifyAPI
   module Rest
@@ -301,6 +302,7 @@ def create_instance(data:, session:, instance: nil)
             end
           end
 
+          instance.original_state = instance.original_state.deep_dup
           instance
         end
       end
diff --git a/test/clients/base_rest_resource_test.rb b/test/clients/base_rest_resource_test.rb
index 78a2e19c8..c090e35e3 100644
--- a/test/clients/base_rest_resource_test.rb
+++ b/test/clients/base_rest_resource_test.rb
@@ -315,6 +315,55 @@ def test_saves_removing_children
         assert_requested(stubbed_request)
       end
 
+      def test_saves_in_place_mutations_to_nested_attributes
+        resource = TestHelpers::FakeResource.create_instance(
+          session: @session,
+          data: {
+            "id" => 1,
+            "details" => { "address" => { "first_name" => "John" }, "tags" => ["original"] },
+          },
+        )
+        stubbed_request = stub_request(:put, "#{@prefix}/fake_resources/1.json")
+          .with(body: hash_including(
+            "fake_resource" => hash_including(
+              "details" => { "address" => { "first_name" => "Jane" } },
+            ),
+          ))
+          .to_return(status: 200)
+
+        resource.details["address"]["first_name"] = "Jane"
+        resource.save
+
+        assert_requested(stubbed_request)
+      end
+
+      def test_preserves_nested_mutations_until_save_succeeds
+        resource = TestHelpers::FakeResource.create_instance(
+          session: @session,
+          data: { "id" => 1, "details" => { "address" => { "first_name" => "John" } } },
+        )
+        resource.details["address"]["first_name"] = "Jane"
+
+        changed_attributes = { "fake_resource" => { "details" => { "address" => { "first_name" => "Jane" } }, "id" => 1 } }
+        changed_request = stub_request(:put, "#{@prefix}/fake_resources/1.json")
+          .with(body: changed_attributes)
+          .to_return(status: 422, body: { errors: "Invalid details" }.to_json)
+          .then
+          .to_return(status: 200, body: { fake_resource: { id: 1, details: { address: { first_name: "Jane" } } } }.to_json)
+
+        assert_raises(ShopifyAPI::Errors::HttpResponseError) { resource.save! }
+        resource.save!
+
+        assert_requested(changed_request, times: 2)
+
+        stubbed_request = stub_request(:put, "#{@prefix}/fake_resources/1.json")
+          .with(body: { "fake_resource" => { "id" => 1 } })
+          .to_return(status: 200)
+        resource.save
+
+        assert_requested(stubbed_request)
+      end
+
       def test_loads_unknown_attribute_with_special_character
         body = { fake_resource: { id: 1, attribute: "attribute", "unknown?": "some-value" } }.to_json