diff --git a/lib/puppet/parser/functions/assert_type.rb b/lib/puppet/parser/functions/assert_type.rb
new file mode 100644
index 000000000..4536cf9aa
--- /dev/null
+++ b/lib/puppet/parser/functions/assert_type.rb
@@ -0,0 +1,30 @@
+Puppet::Parser::Functions::newfunction(
+  :assert_type,
+  :arity => -3,
+  :doc => "Returns the given value if it is an instance of the given type, and raises an error otherwise.
+Optionally, if a block is given (accepting two parameters), it will be called instead of raising
+an error. This to enable giving the user richer feedback, or to supply a default value.
+
+Example: assert that `$b` is a non empty `String` and assign to `$a`:
+
+  $a = assert_type(String[1], $b)
+
+Example using custom error message:
+
+  $a = assert_type(String[1], $b) |$expected, $actual| {
+    fail('The name cannot be empty')
+  }
+
+Example, using a warning and a default:
+
+  $a = assert_type(String[1], $b) |$expected, $actual| {
+    warning('Name is empty, using default')
+    'anonymous'
+  }
+
+See the documentation for 'The Puppet Type System' for more information about types.
+- since Puppet 3.7
+- requires future parser/evaluator
+") do |args|
+  function_fail(["assert_type() is only available when parser/evaluator future is in effect"])
+end