diff --git a/lib/rackstash/encoder/gelf.rb b/lib/rackstash/encoder/gelf.rb
index 80e2968..7991cdf 100644
--- a/lib/rackstash/encoder/gelf.rb
+++ b/lib/rackstash/encoder/gelf.rb
@@ -134,8 +134,10 @@ module Rackstash
 
       def gelf_timestamp(timestamp)
         time = case timestamp
-        when Time, DateTime, Date
+        when Time, DateTime
           timestamp.to_time
+        when Date
+          Time.new(timestamp.year, timestamp.month, timestamp.day, 0, 0, 0, 0)
         when String
           Time.iso8601(timestamp) rescue Time.now.utc
         when Integer, Float
diff --git a/spec/rackstash/encoder/gelf_spec.rb b/spec/rackstash/encoder/gelf_spec.rb
index 435b170..e1e2fb2 100644
--- a/spec/rackstash/encoder/gelf_spec.rb
+++ b/spec/rackstash/encoder/gelf_spec.rb
@@ -55,7 +55,7 @@ RSpec.describe Rackstash::Encoder::GELF do
 
     it 'formats a Date' do
       event = { '@timestamp' => Date.new(2016, 10, 17) }
-      expect(encoder.encode(event)).to include '"timestamp":1476655200.0'
+      expect(encoder.encode(event)).to include '"timestamp":1476662400.0'
     end
 
     it 'formats a String' do