diff --git a/lib/uuid.rb b/lib/uuid.rb
index 6cd9149..8650794 100644
--- a/lib/uuid.rb
+++ b/lib/uuid.rb
@@ -84,7 +84,11 @@ module Version
 
   ##
   # Version number stamped into the UUID to identify it as time-based.
-  VERSION_CLOCK = 0x0100
+  VERSION_CLOCK = 0x1000
+
+  ##
+  # Variant number stamped into the UUID to identify it RFC4211.
+  VARIANT_CLOCK = 0x80
 
   ##
   # Formats supported by the UUID generator.
@@ -95,9 +99,9 @@ module Version
   #                     hyphens
   # <tt>:urn</tt>:: Adds the prefix <tt>urn:uuid:</tt> to the default format
   FORMATS = {
-    :compact => '%08x%04x%04x%04x%012x',
-    :default => '%08x-%04x-%04x-%04x-%012x',
-    :urn     => 'urn:uuid:%08x-%04x-%04x-%04x-%012x',
+    :compact => '%08x%04x%04x%02x%02x%012x',
+    :default => '%08x-%04x-%04x-%02x%02x-%012x',
+    :urn     => 'urn:uuid:%08x-%04x-%04x-%02x%02x-%012x',
   }
 
   ##
@@ -320,7 +324,8 @@ def generate(format = :default)
         clock        & 0xFFFFFFFF,
        (clock >> 32) & 0xFFFF,
       ((clock >> 48) & 0xFFFF | VERSION_CLOCK),
-      @sequence      & 0xFFFF,
+      (@sequence >> 8) & 0xBF | 0x80,
+      @sequence & 0xFF,
       @mac           & 0xFFFFFFFFFFFF
     ]
   end
diff --git a/test/test-uuid.rb b/test/test-uuid.rb
index 335bb0d..968e066 100644
--- a/test/test-uuid.rb
+++ b/test/test-uuid.rb
@@ -56,19 +56,19 @@ def test_with_no_state_file
     UUID.state_file = false
     assert !UUID.state_file
     uuid = UUID.new
-    assert_match(/\A[\da-f]{32}\z/i, uuid.generate(:compact))
+    assert_match(/\A[\da-f]{12}1[\da-f]{3}[89ab][\da-f]{15}\z/i, uuid.generate(:compact))
     seq = uuid.next_sequence
     assert_equal seq + 1, uuid.next_sequence
     assert !UUID.state_file
   end
 
   def validate_uuid_generator(uuid)
-    assert_match(/\A[\da-f]{32}\z/i, uuid.generate(:compact))
+    assert_match(/\A[\da-f]{12}1[\da-f]{3}[89ab][\da-f]{15}\z/i, uuid.generate(:compact))
 
-    assert_match(/\A[\da-f]{8}-[\da-f]{4}-[\da-f]{4}-[\da-f]{4}-[\da-f]{12}\z/i,
+    assert_match(/\A[\da-f]{8}-[\da-f]{4}-1[\da-f]{3}-[89ab][\da-f]{3}-[\da-f]{12}\z/i,
                  uuid.generate(:default))
 
-    assert_match(/^urn:uuid:[\da-f]{8}-[\da-f]{4}-[\da-f]{4}-[\da-f]{4}-[\da-f]{12}\z/i,
+    assert_match(/^urn:uuid:[\da-f]{8}-[\da-f]{4}-1[\da-f]{3}-[89ab][\da-f]{3}-[\da-f]{12}\z/i,
                  uuid.generate(:urn))
 
     e = assert_raise ArgumentError do
@@ -84,12 +84,12 @@ def test_instance_generate
   end
 
   def test_class_generate
-    assert_match(/\A[\da-f]{32}\z/i, UUID.generate(:compact))
+    assert_match(/\A[\da-f]{12}1[\da-f]{3}[89ab][\da-f]{15}\z/i, UUID.generate(:compact))
 
-    assert_match(/\A[\da-f]{8}-[\da-f]{4}-[\da-f]{4}-[\da-f]{4}-[\da-f]{12}\z/i,
+    assert_match(/\A[\da-f]{8}-[\da-f]{4}-1[\da-f]{3}-[89ab][\da-f]{3}-[\da-f]{12}\z/i,
                  UUID.generate(:default))
 
-    assert_match(/^urn:uuid:[\da-f]{8}-[\da-f]{4}-[\da-f]{4}-[\da-f]{4}-[\da-f]{12}\z/i,
+    assert_match(/^urn:uuid:[\da-f]{8}-[\da-f]{4}-1[\da-f]{3}-[89ab][\da-f]{3}-[\da-f]{12}\z/i,
                  UUID.generate(:urn))
 
     e = assert_raise ArgumentError do