diff --git a/lib/ulid.ex b/lib/ulid.ex
index 89a40c0..58463db 100644
--- a/lib/ulid.ex
+++ b/lib/ulid.ex
@@ -1,9 +1,9 @@
 defmodule Ulid do
-  def generate(timestamp \\ System.system_time(:milli_seconds)) do
+  def generate(timestamp \\ System.system_time(:millisecond)) do
     Ulid.Utils.encode(generate_binary(timestamp))
   end
 
-  def generate_binary(timestamp \\ System.system_time(:milli_seconds)) do
+  def generate_binary(timestamp \\ System.system_time(:millisecond)) do
     <<timestamp::unsigned-size(48), :crypto.strong_rand_bytes(10)::binary>>
   end
 end