diff --git a/lib/thin/headers.rb b/lib/thin/headers.rb
index ba0f95a4..3e1b9cc3 100644
--- a/lib/thin/headers.rb
+++ b/lib/thin/headers.rb
@@ -18,7 +18,7 @@ def []=(key, value)
         @sent[key] = true
         value = case value
                 when Time
-                  value.rfc822
+                  value.httpdate
                 when NilClass
                   return
                 else
diff --git a/spec/headers_spec.rb b/spec/headers_spec.rb
index 87ab099e..98ee4709 100644
--- a/spec/headers_spec.rb
+++ b/spec/headers_spec.rb
@@ -35,6 +35,6 @@
   it 'should format Time values correctly' do
     time = Time.now
     @headers['Modified-At'] = time
-    @headers.to_s.should include("Modified-At: #{time.rfc822}")
+    @headers.to_s.should include("Modified-At: #{time.httpdate}")
   end
 end
\ No newline at end of file