diff --git a/lib/rackstash.rb b/lib/rackstash.rb
index b0bdb44..051ed06 100644
--- a/lib/rackstash.rb
+++ b/lib/rackstash.rb
@@ -66,7 +66,7 @@ module Rackstash
   EMPTY_SET = Set.new.freeze
 
   # How many decimal places to render on ISO 8601 timestamps
-  ISO8601_PRECISION = 3
+  ISO8601_PRECISION = 6
 
   FIELD_MESSAGE = 'message'.freeze
   FIELD_TAGS = 'tags'.freeze
diff --git a/spec/rackstash/buffer_spec.rb b/spec/rackstash/buffer_spec.rb
index d00d366..3d0709d 100644
--- a/spec/rackstash/buffer_spec.rb
+++ b/spec/rackstash/buffer_spec.rb
@@ -33,7 +33,7 @@ describe Rackstash::Buffer do
       msg = double(message: 'Hello World', time: time)
 
       buffer.add_message msg
-      expect(buffer.timestamp).to eql '2016-10-17T10:37:00.000Z'
+      expect(buffer.timestamp).to eql '2016-10-17T10:37:00.000000Z'
     end
 
     context 'when buffering?' do
@@ -111,12 +111,12 @@ describe Rackstash::Buffer do
 
     it 'resets the timestamp' do
       buffer.timestamp(Time.parse('2016-10-17 15:37:00 +02:00'))
-      expect(buffer.timestamp).to eql '2016-10-17T13:37:00.000Z'
+      expect(buffer.timestamp).to eql '2016-10-17T13:37:00.000000Z'
 
       buffer.clear
 
       expect(Time).to receive(:now).and_call_original
-      expect(buffer.timestamp).not_to eql '2016-10-17T13:37:00.000Z'
+      expect(buffer.timestamp).not_to eql '2016-10-17T13:37:00.000000Z'
     end
   end
 
@@ -306,16 +306,16 @@ describe Rackstash::Buffer do
       expect(Time).to receive(:now).once.and_return(now)
       expect(now).to receive(:getutc).once.and_return(now.getutc)
 
-      expect(buffer.timestamp).to eql '2016-10-17T10:37:00.000Z'
-      expect(buffer.timestamp).to eql '2016-10-17T10:37:00.000Z'
+      expect(buffer.timestamp).to eql '2016-10-17T10:37:00.000000Z'
+      expect(buffer.timestamp).to eql '2016-10-17T10:37:00.000000Z'
     end
 
     it 'initializes @timestamp with the passed time' do
       now = Time.parse('2016-10-17 13:37:00 +03:00')
 
       expect(Time).not_to receive(:now)
-      expect(buffer.timestamp(now)).to eql '2016-10-17T10:37:00.000Z'
-      expect(buffer.timestamp).to eql '2016-10-17T10:37:00.000Z'
+      expect(buffer.timestamp(now)).to eql '2016-10-17T10:37:00.000000Z'
+      expect(buffer.timestamp).to eql '2016-10-17T10:37:00.000000Z'
     end
 
     it 'does not overwrites an already set timestamp' do
@@ -323,13 +323,13 @@ describe Rackstash::Buffer do
       second = Time.parse('2016-10-17 20:20:20 +03:00')
 
       buffer.timestamp(first)
-      expect(buffer.timestamp).to eql '2016-10-17T07:10:10.000Z'
+      expect(buffer.timestamp).to eql '2016-10-17T07:10:10.000000Z'
 
       buffer.timestamp
-      expect(buffer.timestamp).to eql '2016-10-17T07:10:10.000Z'
+      expect(buffer.timestamp).to eql '2016-10-17T07:10:10.000000Z'
 
       buffer.timestamp(second)
-      expect(buffer.timestamp).to eql '2016-10-17T07:10:10.000Z'
+      expect(buffer.timestamp).to eql '2016-10-17T07:10:10.000000Z'
     end
   end
 end
diff --git a/spec/rackstash/fields/abstract_collection_spec.rb b/spec/rackstash/fields/abstract_collection_spec.rb
index 7a8f017..843c5cd 100644
--- a/spec/rackstash/fields/abstract_collection_spec.rb
+++ b/spec/rackstash/fields/abstract_collection_spec.rb
@@ -356,7 +356,7 @@ describe Rackstash::Fields::AbstractCollection do
     it 'formats Time as an ISO 8601 UTC timestamp' do
       time = Time.parse('2016-10-17 16:37:42 +03:00')
 
-      expect(normalize(time)).to eql '2016-10-17T13:37:42.000Z'
+      expect(normalize(time)).to eql '2016-10-17T13:37:42.000000Z'
       expect(normalize(time).encoding).to eql Encoding::UTF_8
       expect(normalize(time)).to be_frozen
     end
@@ -364,7 +364,7 @@ describe Rackstash::Fields::AbstractCollection do
     it 'formats DateTime as an ISO 8601 UTC timestamp' do
       datetime = DateTime.parse('2016-10-17 15:37:42 CEST') # UTC +02:00
 
-      expect(normalize(datetime)).to eql '2016-10-17T13:37:42.000Z'
+      expect(normalize(datetime)).to eql '2016-10-17T13:37:42.000000Z'
       expect(normalize(datetime).encoding).to eql Encoding::UTF_8
       expect(normalize(datetime)).to be_frozen
     end