diff --git a/lib/puppet/functions/assert_type.rb b/lib/puppet/functions/assert_type.rb
index 189d36419..5d0a70e09 100644
--- a/lib/puppet/functions/assert_type.rb
+++ b/lib/puppet/functions/assert_type.rb
@@ -1,25 +1,29 @@
 # Returns the given value if it is an instance of the given type, and raises an error otherwise.
 #
 # @example how to assert type
 #   # assert that `$b` is a non empty `String` and assign to `$a`
 #   $a = assert_type(String[1], $b)
 #
 # See the documentation for "The Puppet Type System" for more information about types.
 #
 Puppet::Functions.create_function(:assert_type) do
   dispatch :assert_type do
     param type_type(), 'type'
     param optional(object()), 'value'
   end
 
   # @param type [Type] the type the value must be an instance of
   # @param value [Optional[Object]] the value to assert
   #
   def assert_type(type, value)
     unless Puppet::Pops::Types::TypeCalculator.instance?(type,value)
       inferred_type = Puppet::Pops::Types::TypeCalculator.infer(value)
-      raise ArgumentError, "assert_type(): Expected type #{type} does not match actual: #{inferred_type}"
+      # Do not give all the details - i.e. format as Integer, instead of Integer[n, n] for exact value, which
+      # is just confusing. (OTOH: may need to revisit, or provide a better "type diff" output.
+      #
+      actual = Puppet::Pops::Types::TypeCalculator.generalize!(inferred_type)
+      raise Puppet::ParseError, "assert_type(): Expected type #{type} does not match actual: #{actual}"
     end
     value
   end
 end