diff --git a/lib/puppet/functions/flatten_to_argument_list.rb b/lib/puppet/functions/flatten_to_argument_list.rb
new file mode 100644
index 0000000..a718f8d
--- /dev/null
+++ b/lib/puppet/functions/flatten_to_argument_list.rb
@@ -0,0 +1,35 @@
+require 'shellwords'
+
+Puppet::Functions.create_function(:flatten_to_argument_list) do
+  dispatch :flatten_to_argument_list do
+    param 'Hash', :variable
+    optional_param 'String', :escaping_type
+    optional_param 'String', :prefix
+    return_type 'Array[String]'
+  end
+
+  def flatten_to_argument_list(variable, escaping_type = 'systemd', prefix = '--')
+    ret = []
+    variable.each do |key, value|
+      arg = "#{prefix}#{key}".gsub('_', '-')
+      if Hash === value
+        ret += flatten_to_argument_list(value, escaping_type, "#{arg}.")
+      else
+        if value == true
+          ret.push(arg)
+        else
+          if escaping_type == 'systemd'
+            # This replaces every backslash with four backslashes to please
+            # systemd's EnvironmentFile escaping. Yes, gsub needs four
+            # backslashes per output backslash.
+            value.gsub!('\\', '\\\\\\\\\\\\\\\\')
+          elsif escaping_type == 'shell'
+            value = Shellwords.escape(value)
+          end
+          ret.push("#{arg}=#{value}")
+        end
+      end
+    end
+    ret
+  end
+end