diff --git a/Gemfile b/Gemfile
index f25683b..d8f7789 100644
--- a/Gemfile
+++ b/Gemfile
@@ -13,3 +13,5 @@ gem "rubocop", "~> 1.21"
 
 gem "debug"
 gem "sqlite3"
+
+gem "actionpack"
diff --git a/Gemfile.lock b/Gemfile.lock
index d5c55ce..79236a5 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -9,6 +9,22 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
+    actionpack (8.0.2)
+      actionview (= 8.0.2)
+      activesupport (= 8.0.2)
+      nokogiri (>= 1.8.5)
+      rack (>= 2.2.4)
+      rack-session (>= 1.0.1)
+      rack-test (>= 0.6.3)
+      rails-dom-testing (~> 2.2)
+      rails-html-sanitizer (~> 1.6)
+      useragent (~> 0.16)
+    actionview (8.0.2)
+      activesupport (= 8.0.2)
+      builder (~> 3.1)
+      erubi (~> 1.11)
+      rails-dom-testing (~> 2.2)
+      rails-html-sanitizer (~> 1.6)
     activemodel (8.0.2)
       activesupport (= 8.0.2)
     activerecord (8.0.2)
@@ -32,13 +48,16 @@ GEM
     base64 (0.2.0)
     benchmark (0.4.0)
     bigdecimal (3.1.9)
+    builder (3.3.0)
     concurrent-ruby (1.3.5)
     connection_pool (2.5.3)
+    crass (1.0.6)
     date (3.4.1)
     debug (1.10.0)
       irb (~> 1.10)
       reline (>= 0.3.8)
     drb (2.2.1)
+    erubi (1.13.1)
     i18n (1.14.7)
       concurrent-ruby (~> 1.0)
     io-console (0.8.0)
@@ -50,8 +69,16 @@ GEM
     language_server-protocol (3.17.0.4)
     lint_roller (1.1.0)
     logger (1.7.0)
+    loofah (2.24.1)
+      crass (~> 1.0.2)
+      nokogiri (>= 1.12.0)
     mini_portile2 (2.8.8)
     minitest (5.25.5)
+    nokogiri (1.18.9)
+      mini_portile2 (~> 2.8.2)
+      racc (~> 1.4)
+    nokogiri (1.18.9-arm64-darwin)
+      racc (~> 1.4)
     parallel (1.27.0)
     parser (3.3.8.0)
       ast (~> 2.4.1)
@@ -64,6 +91,19 @@ GEM
       date
       stringio
     racc (1.8.1)
+    rack (3.2.0)
+    rack-session (2.1.1)
+      base64 (>= 0.1.0)
+      rack (>= 3.0.0)
+    rack-test (2.2.0)
+      rack (>= 1.3)
+    rails-dom-testing (2.3.0)
+      activesupport (>= 5.0.0)
+      minitest
+      nokogiri (>= 1.6)
+    rails-html-sanitizer (1.6.2)
+      loofah (~> 2.21)
+      nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
     rainbow (3.1.1)
     rake (13.2.1)
     rdoc (6.13.1)
@@ -98,12 +138,14 @@ GEM
       unicode-emoji (~> 4.0, >= 4.0.4)
     unicode-emoji (4.0.4)
     uri (1.0.3)
+    useragent (0.16.11)
 
 PLATFORMS
   arm64-darwin-23
   ruby
 
 DEPENDENCIES
+  actionpack
   debug
   minitest (~> 5.16)
   rake (~> 13.0)
diff --git a/lib/trenchcoat.rb b/lib/trenchcoat.rb
index 670f8ed..822108b 100644
--- a/lib/trenchcoat.rb
+++ b/lib/trenchcoat.rb
@@ -9,8 +9,9 @@ module Model
     extend ActiveSupport::Concern
 
     def fallback_to_model_values(model:, attributes_to_check:, original_attributes_hash:)
+      indifferent_original_attributes = original_attributes_hash.to_h.with_indifferent_access
       attributes_to_check.each do |attribute|
-        next if original_attributes_hash.with_indifferent_access.key?(attribute)
+        next if indifferent_original_attributes.key?(attribute)
 
         send(:"#{attribute}=", model.public_send(attribute))
       end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 3c21cb7..434da45 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -3,6 +3,7 @@
 $LOAD_PATH.unshift File.expand_path("../lib", __dir__)
 require "trenchcoat"
 require "active_record"
+require "action_controller"
 require "debug"
 
 ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
diff --git a/test/test_trenchcoat.rb b/test/test_trenchcoat.rb
index 29fda4f..e168ee7 100644
--- a/test/test_trenchcoat.rb
+++ b/test/test_trenchcoat.rb
@@ -111,6 +111,23 @@ def normalize_published_at
       assert_equal true, form.is_published
     end
 
+    test "fallback_to_model_values: given ActionController::Parameters" do
+      time = Time.utc(2021, 2, 2)
+      post = Post.create!(title: "A Post", body: "Post Content")
+
+      parameters = ActionController::Parameters.new(title: "Hello", published_at: time, is_published: "1").permit(
+        :title, :body, :published_at
+      ).merge(post: post)
+
+      form = CustomForm.new(parameters)
+
+      assert_equal post, form.post
+      assert_equal "Hello", form.title
+      assert_equal "Post Content", form.body
+      assert_equal time, form.published_at
+      assert_equal true, form.is_published
+    end
+
     test "creating a new record, updating" do
       form = CustomForm.new
       form.title = SecureRandom.hex