diff --git a/REFERENCE.md b/REFERENCE.md
index 0d78da93d..0122b9020 100644
--- a/REFERENCE.md
+++ b/REFERENCE.md
@@ -4578,6 +4578,14 @@ file { '/tmp/my.yaml':
 }
 ```
 
+##### Sort keys for stable output
+
+```puppet
+file { '/tmp/my.yaml':
+  ensure  => file,
+  content => stdlib::to_yaml($myhash, {sort_keys => true})
+```
+
 #### `stdlib::to_yaml(Any $data, Optional[Hash] $options)`
 
 Convert a data structure and output it as YAML
@@ -4604,6 +4612,14 @@ file { '/tmp/my.yaml':
 }
 ```
 
+###### Sort keys for stable output
+
+```puppet
+file { '/tmp/my.yaml':
+  ensure  => file,
+  content => stdlib::to_yaml($myhash, {sort_keys => true})
+```
+
 ##### `data`
 
 Data type: `Any`
diff --git a/lib/puppet/functions/stdlib/to_yaml.rb b/lib/puppet/functions/stdlib/to_yaml.rb
index ab162cd8b..92f330d2d 100644
--- a/lib/puppet/functions/stdlib/to_yaml.rb
+++ b/lib/puppet/functions/stdlib/to_yaml.rb
@@ -19,6 +19,10 @@
   #     ensure  => file,
   #     content => stdlib::to_yaml($myhash, {indentation => 4})
   #   }
+  # @example Sort keys for stable output
+  #   file { '/tmp/my.yaml':
+  #     ensure  => file,
+  #     content => stdlib::to_yaml($myhash, {sort_keys => true})
   #
   # @return [String] The YAML document
   dispatch :to_yaml do
@@ -28,7 +32,33 @@
 
   def to_yaml(data, options = {})
     call_function('stdlib::rewrap_sensitive_data', data) do |unwrapped_data|
-      unwrapped_data.to_yaml(options.transform_keys(&:to_sym))
+      # 1) build a fresh, mutable hash of options
+      #    transform_keys returns a new hash in Ruby 2.5+
+      opts = options.transform_keys(&:to_sym)
+
+      # 2) pluck out our custom flag (default false)
+      sort_keys = opts.delete(:sort_keys) || false
+
+      # 3) sort if requested
+      unwrapped_data = deep_sort(unwrapped_data) if sort_keys
+
+      # 4) dump with the remaining opts
+      unwrapped_data.to_yaml(opts)
+    end
+  end
+
+  private
+
+  def deep_sort(obj)
+    case obj
+    when Hash
+      # sort returns an Array of [k,v], then to_h makes a new Hash
+      obj.sort.to_h { |k, v| [k, deep_sort(v)] }
+    when Array
+      # preserve list order, but recurse into elements
+      obj.map { |item| deep_sort(item) }
+    else
+      obj
     end
   end
 end
diff --git a/spec/functions/to_yaml_spec.rb b/spec/functions/to_yaml_spec.rb
index edaceb877..0332a77c9 100644
--- a/spec/functions/to_yaml_spec.rb
+++ b/spec/functions/to_yaml_spec.rb
@@ -4,26 +4,119 @@
 
 describe 'stdlib::to_yaml' do
   it { is_expected.not_to be_nil }
+
+  # Basic scalars
   it { is_expected.to run.with_params('').and_return("--- ''\n") }
-  it { is_expected.to run.with_params(true).and_return(%r{--- true\n}) }
-  it { is_expected.to run.with_params('one').and_return(%r{--- one\n}) }
+  it { is_expected.to run.with_params(true).and_return("--- true\n") }
+  it { is_expected.to run.with_params(false).and_return("--- false\n") }
+  it { is_expected.to run.with_params(42).and_return("--- 42\n") }
+  it { is_expected.to run.with_params('one').and_return("--- one\n") }
+
+  # Unicode
+  it { is_expected.to run.with_params('‰').and_return("--- \"‰\"\n") }
+  it { is_expected.to run.with_params('∇').and_return("--- \"∇\"\n") }
+
+  # Arrays
   it { is_expected.to run.with_params([]).and_return("--- []\n") }
   it { is_expected.to run.with_params(['one']).and_return("---\n- one\n") }
   it { is_expected.to run.with_params(['one', 'two']).and_return("---\n- one\n- two\n") }
+
+  # Hashes
   it { is_expected.to run.with_params({}).and_return("--- {}\n") }
   it { is_expected.to run.with_params('key' => 'value').and_return("---\nkey: value\n") }
 
+  # Nested structures
   it {
-    expect(subject).to run.with_params('one' => { 'oneA' => 'A', 'oneB' => { 'oneB1' => '1', 'oneB2' => '2' } }, 'two' => ['twoA', 'twoB'])
-                          .and_return("---\none:\n  oneA: A\n  oneB:\n    oneB1: '1'\n    oneB2: '2'\ntwo:\n- twoA\n- twoB\n")
+    is_expected.to run.with_params(
+      'one' => { 'oneA' => 'A', 'oneB' => { 'oneB1' => '1', 'oneB2' => '2' } },
+      'two' => ['twoA', 'twoB'],
+    ).and_return("---\none:\n  oneA: A\n  oneB:\n    oneB1: '1'\n    oneB2: '2'\ntwo:\n- twoA\n- twoB\n")
   }
 
-  it { is_expected.to run.with_params('‰').and_return("--- \"‰\"\n") }
-  it { is_expected.to run.with_params('∇').and_return("--- \"∇\"\n") }
+  # Options: indentation
+  it {
+    is_expected.to run.with_params(
+      { 'foo' => { 'bar' => true, 'baz' => false } },
+      'indentation' => 4,
+    ).and_return("---\nfoo:\n    bar: true\n    baz: false\n")
+  }
+
+  # Frozen options hash must not raise
+  it {
+    is_expected.to run.with_params(
+      { 'foo' => { 'bar' => true } },
+      { 'indentation' => 4, 'sort_keys' => true }.freeze,
+    ).and_return("---\nfoo:\n    bar: true\n")
+  }
+
+  # sort_keys: default behaviour preserves insertion order
+  it {
+    is_expected.to run.with_params(
+      'z' => 1, 'a' => 2, 'm' => 3,
+    ).and_return("---\nz: 1\na: 2\nm: 3\n")
+  }
+
+  # sort_keys => true: top-level keys sorted
+  it {
+    is_expected.to run.with_params(
+      { 'z' => 1, 'a' => 2, 'm' => 3 },
+      'sort_keys' => true,
+    ).and_return("---\na: 2\nm: 3\nz: 1\n")
+  }
 
-  it { is_expected.to run.with_params({ 'foo' => { 'bar' => true, 'baz' => false } }, 'indentation' => 4).and_return("---\nfoo:\n    bar: true\n    baz: false\n") }
+  # sort_keys => true: nested keys sorted
+  it {
+    is_expected.to run.with_params(
+      { 'parent' => { 'z' => 1, 'a' => 2 } },
+      'sort_keys' => true,
+    ).and_return("---\nparent:\n  a: 2\n  z: 1\n")
+  }
 
+  # sort_keys => true: deeply nested keys sorted
+  it {
+    is_expected.to run.with_params(
+      { 'z_parent' => { 'z_child' => 1, 'a_child' => 2 }, 'a_parent' => { 'x' => 5 } },
+      'sort_keys' => true,
+    ).and_return("---\na_parent:\n  x: 5\nz_parent:\n  a_child: 2\n  z_child: 1\n")
+  }
+
+  # sort_keys => true: array order preserved, hashes inside arrays sorted
+  it {
+    is_expected.to run.with_params(
+      { 'items' => [{ 'z' => 1, 'a' => 2 }, { 'x' => 3, 'b' => 4 }] },
+      'sort_keys' => true,
+    ).and_return("---\nitems:\n- a: 2\n  z: 1\n- b: 4\n  x: 3\n")
+  }
+
+  # sort_keys => true: plain array element order preserved
+  it {
+    is_expected.to run.with_params(
+      { 'items' => [3, 1, 2] },
+      'sort_keys' => true,
+    ).and_return("---\nitems:\n- 3\n- 1\n- 2\n")
+  }
+
+  # sort_keys combined with indentation
+  it {
+    is_expected.to run.with_params(
+      { 'z' => { 'b' => 1, 'a' => 2 }, 'a' => 3 },
+      'sort_keys' => true, 'indentation' => 4,
+    ).and_return("---\na: 3\nz:\n    a: 2\n    b: 1\n")
+  }
+
+  # Sensitive data
   context 'with data containing sensitive' do
-    it { is_expected.to run.with_params('key' => sensitive('value')).and_return(sensitive("---\nkey: value\n")) }
+    it {
+      is_expected.to run.with_params(
+        'key' => sensitive('value'),
+      ).and_return(sensitive("---\nkey: value\n"))
+    }
+
+    it {
+      is_expected.to run.with_params(
+        { 'z' => sensitive('secret'), 'a' => 'public' },
+        'sort_keys' => true,
+      ).and_return(sensitive("---\na: public\nz: secret\n"))
+    }
   end
 end