diff --git a/Gemfile.lock b/Gemfile.lock
index 618f71e..8987e2f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,17 +1,17 @@
 PATH
   remote: .
   specs:
-    uuid (2.3.7)
+    uuid (2.3.9)
       macaddr (~> 1.0)
 
 GEM
   remote: https://rubygems.org/
   specs:
-    macaddr (1.6.7)
+    macaddr (1.7.1)
       systemu (~> 2.6.2)
     mocha (0.9.12)
     rake (0.8.7)
-    systemu (2.6.4)
+    systemu (2.6.5)
     yard (0.6.7)
 
 PLATFORMS
diff --git a/lib/uuid.rb b/lib/uuid.rb
index 6cd9149..7d0447b 100644
--- a/lib/uuid.rb
+++ b/lib/uuid.rb
@@ -84,7 +84,23 @@ module Version
 
   ##
   # Version number stamped into the UUID to identify it as time-based.
-  VERSION_CLOCK = 0x0100
+  VERSION_CLOCK = 0x1000
+
+  ##
+  # Time.at(UUID_EPOCH_OFFSET / -1e7).utc == 1582-10-15 00:00:00 UTC.
+  UUID_EPOCH_OFFSET = 0x01B21DD213814000
+
+  ##
+  # Get time as 100ns ticks since UUID epoch.
+  if Process.respond_to?(:clock_gettime)
+    def uuid_tick
+      Process.clock_gettime(Process::CLOCK_REALTIME, :nanosecond) / 100 + UUID_EPOCH_OFFSET
+    end
+  else
+    def uuid_tick
+      (Time.now.to_f * 10_000_000).to_i + UUID_EPOCH_OFFSET
+    end
+  end
 
   ##
   # Formats supported by the UUID generator.
@@ -255,7 +271,7 @@ def mac_address
   # Create a new UUID generator.  You really only need to do this once.
   def initialize
     @drift = 0
-    @last_clock = (Time.now.to_f * CLOCK_MULTIPLIER).to_i
+    @last_clock = uuid_tick
     @mutex = Mutex.new
 
     state_file = self.class.state_file
@@ -296,7 +312,7 @@ def generate(format = :default)
     # with the new clock.
 
     clock = @mutex.synchronize do
-      clock = (Time.new.to_f * CLOCK_MULTIPLIER).to_i & 0xFFFFFFFFFFFFFFF0
+      clock = uuid_tick & 0xFFFFFFFFFFFFFFF0
 
       if clock > @last_clock then
         @drift = 0
@@ -319,8 +335,8 @@ def generate(format = :default)
     template % [
         clock        & 0xFFFFFFFF,
        (clock >> 32) & 0xFFFF,
-      ((clock >> 48) & 0xFFFF | VERSION_CLOCK),
-      @sequence      & 0xFFFF,
+      ((clock >> 48) & 0x0FFF) | VERSION_CLOCK,
+      (@sequence     & 0x3FFF) | 0x8000,
       @mac           & 0xFFFFFFFFFFFF
     ]
   end
@@ -347,7 +363,7 @@ def next_sequence
       write_state io
     end
   ensure
-    @last_clock = (Time.now.to_f * CLOCK_MULTIPLIER).to_i
+    @last_clock = uuid_tick
     @drift = 0
   end
 
diff --git a/test/test-uuid.rb b/test/test-uuid.rb
index 335bb0d..9198379 100644
--- a/test/test-uuid.rb
+++ b/test/test-uuid.rb
@@ -143,6 +143,28 @@ class << bar = UUID.new
     assert_equal foo.sequence + 1, bar.sequence
   end
 
+  def test_uuidv1_fixed_bits
+    uuid = UUID.generate(:default)
+    v = uuid.gsub("-", "").to_i(16)
+    assert_equal(
+      "%x" % [0x00000000_0000_1000_8000_000000000000],
+      "%x" % [0x00000000_0000_f000_c000_000000000000 & v],
+      "unexpected bits in #{uuid}")
+  end
+
+  def test_uuidv1_time_field
+    t1 = Time.now.to_f
+    uuid = UUID.generate(:default)
+    t2 = Time.now.to_f
+    v = uuid.gsub("-", "").to_i(16)
+    time_field = (
+      (((v >> 64) & 0x0fff) << 48) |
+      (((v >> 80) & 0xffff) << 32) |
+      ((v >> 96) & 0xffff_ffff))
+    t = time_field * 1e-7 - 12219292800
+    assert_equal true, (t1 <= t && t <= t2), "invalid time in #{uuid}"
+  end
+
   def test_pseudo_random_mac_address
     uuid_gen = UUID.new
     Mac.stubs(:addr).returns "00:00:00:00:00:00"