diff --git a/README.md b/README.md
index af29146..8284e93 100644
--- a/README.md
+++ b/README.md
@@ -58,7 +58,7 @@ ULID.generate
 You can also input a seed time which will consistently give you the same string for the time component. This is useful for migrating to ulid.
 
 ```crystal
-ULID.generate Time.now + 5.second
+ULID.generate Time.utc + 5.second
 # => "01ARYZ6S41TSV4RRFFQ69G5FAV"
 ```
 
diff --git a/spec/ulid_spec.cr b/spec/ulid_spec.cr
index 994fa71..9c58e01 100644
--- a/spec/ulid_spec.cr
+++ b/spec/ulid_spec.cr
@@ -51,7 +51,7 @@ describe ULID do
       1000.times do
         ulid_1 = ULID.generate
         sleep 1.millisecond
-        ulid_2 = ULID.generate(Time.now - 1.second)
+        ulid_2 = ULID.generate(Time.utc - 1.second)
 
         (ulid_2 < ulid_1).should be_true
       end
diff --git a/src/ulid.cr b/src/ulid.cr
index bead01c..2bf7658 100644
--- a/src/ulid.cr
+++ b/src/ulid.cr
@@ -15,18 +15,18 @@ module ULID
   # ULID.generate
   # # => "01B3EAF48P97R8MP9WS6MHDTZ3"
   # ```
-  def generate(seed_time : Time = Time.now) : String
+  def generate(seed_time : Time = Time.utc) : String
     encode_time(seed_time, TIME_LEN) + encode_random(RANDOM_LEN)
   end
 
   private def encode_time(now : Time, len : Int32) : String
-    ms = now.epoch_ms
+    ms = now.to_unix_ms
 
     String.build do |io|
       len.times do |i|
         mod = ms % ENCODING_LEN
         io << ENCODING[mod]
-        ms = (ms - mod) / ENCODING_LEN
+        ms = (ms - mod) // ENCODING_LEN
       end
     end.reverse
   end