diff --git a/railties/lib/rails/commands/credentials/credentials_command.rb b/railties/lib/rails/commands/credentials/credentials_command.rb
index 1da5cc29e16..75a832ab4a2 100644
--- a/railties/lib/rails/commands/credentials/credentials_command.rb
+++ b/railties/lib/rails/commands/credentials/credentials_command.rb
@@ -128,7 +128,11 @@ module Rails
         end
 
         def extract_environment_from_path(path)
-          available_environments.find { |env| path.end_with?("#{env}.yml.enc") }
+          available_environments.find { |env| path.end_with?("#{env}.yml.enc") } || extract_custom_environment(path)
+        end
+
+        def extract_custom_environment(path)
+          path =~ %r{config/credentials/(.+)\.yml\.enc} && $1
         end
     end
   end
diff --git a/railties/test/commands/credentials_test.rb b/railties/test/commands/credentials_test.rb
index 4b29ed656fc..45ebd886ead 100644
--- a/railties/test/commands/credentials_test.rb
+++ b/railties/test/commands/credentials_test.rb
@@ -285,6 +285,20 @@ class Rails::Command::CredentialsTest < ActiveSupport::TestCase
     assert_match(raw_content, run_diff_command("config/credentials.yml.enc"))
   end
 
+  test "diff for custom environment" do
+    run_edit_command(environment: "custom")
+
+    assert_match(/access_key_id: 123/, run_diff_command("config/credentials/custom.yml.enc"))
+  end
+
+  test "diff for custom environment when key is not available" do
+    run_edit_command(environment: "custom")
+    remove_file "config/credentials/custom.key"
+
+    raw_content = File.read(app_path("config", "credentials", "custom.yml.enc"))
+    assert_match(raw_content, run_diff_command("config/credentials/custom.yml.enc"))
+  end
+
   test "diff returns raw encrypted content when errors occur" do
     run_edit_command(environment: "development")