diff --git a/lib/net/dns/header.rb b/lib/net/dns/header.rb
index 2681d35..5ea95cb 100644
--- a/lib/net/dns/header.rb
+++ b/lib/net/dns/header.rb
@@ -63,10 +63,6 @@ class WrongOpcodeError < ArgumentError
       class Error < StandardError
       end
 
-      # The requested ID is already in use.
-      class DuplicateIDError < Error
-      end
-
 
       #
       # = Name
@@ -180,8 +176,6 @@ def to_s
       # Array with given strings
       OPARR = %w[QUERY IQUERY STATUS]
 
-      @@id_arr = []
-
       # Reader for +id+ attribute
       attr_reader :id
       # Reader for the operational code
@@ -357,12 +351,8 @@ def data
       # performing security tests.
       #
       def id=(val)
-        if @@id_arr.include? val
-          raise DuplicateIDError, "ID `#{val}' already used"
-        end
         if (1..65535).include? val
           @id = val
-          @@id_arr.push val
         else
           raise ArgumentError, "ID `#{val}' out of range"
         end
@@ -729,10 +719,7 @@ def new_from_hash(hash)
       end
 
       def genID
-        while (@@id_arr.include?(q = rand(65535)))
-        end
-        @@id_arr.push(q)
-        q
+        rand(65535)
       end
 
     end
diff --git a/test/header_test.rb b/test/header_test.rb
index 16c3fec..cba7dfe 100644
--- a/test/header_test.rb
+++ b/test/header_test.rb
@@ -119,9 +119,6 @@ def test_simple
     assert_raises(ArgumentError) do
       Header.parse("aa")
     end
-    assert_raises(Header::DuplicateIDError) do
-      @default.id = 441
-    end
     assert_raises(ArgumentError) do
       @default.id = 1000000
     end