diff --git a/protocols/shared/src/main/scala-2/fs2/protocols/ntp/NTPPacketCompat.scala b/protocols/shared/src/main/scala-2/fs2/protocols/ntp/NTPPacketCompat.scala
new file mode 100644
index 0000000000..6463e11605
--- /dev/null
+++ b/protocols/shared/src/main/scala-2/fs2/protocols/ntp/NTPPacketCompat.scala
@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2013 Functional Streams for Scala
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package fs2.protocols.ntp
+
+import org.typelevel.scalaccompat.annotation.*
+import scodec.*
+import shapeless.Generic
+import shapeless.Nat
+@nowarn3("msg=unused import")
+private[ntp] trait NTPPacketCompat { self: NTPPacket.type =>
+  import scodec.compat.*
+  def codec: Codec[NTPPacket] = layout
+    .xmap(
+      { case liVnMode *: rest =>
+        Generic[NTPPacket].from(liVnMode ++ rest)
+      },
+      Generic[NTPPacket].to(_).split[Nat._3] match {
+        case (liVnMode, rest) => liVnMode *: rest
+      }
+    )
+}
diff --git a/protocols/shared/src/main/scala-3/fs2/protocols/ntp/NTPPacketCompat.scala b/protocols/shared/src/main/scala-3/fs2/protocols/ntp/NTPPacketCompat.scala
new file mode 100644
index 0000000000..1707199445
--- /dev/null
+++ b/protocols/shared/src/main/scala-3/fs2/protocols/ntp/NTPPacketCompat.scala
@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2013 Functional Streams for Scala
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package fs2.protocols.ntp
+
+import scodec.*
+import scala.deriving.Mirror
+
+private[ntp] trait NTPPacketCompat { self: NTPPacket.type =>
+  def codec: Codec[NTPPacket] = layout
+    .xmap(
+      { case liVnMode *: rest =>
+        summon[Mirror.ProductOf[NTPPacket]].fromProduct(liVnMode ++ rest)
+      },
+      Tuple.fromProductTyped(_).splitAt(3) match {
+        case (liVnMode, rest) => liVnMode *: rest
+      }
+    )
+}
diff --git a/protocols/shared/src/main/scala/fs2/protocols/ntp/LeapIndicator.scala b/protocols/shared/src/main/scala/fs2/protocols/ntp/LeapIndicator.scala
new file mode 100644
index 0000000000..9c787a61db
--- /dev/null
+++ b/protocols/shared/src/main/scala/fs2/protocols/ntp/LeapIndicator.scala
@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2013 Functional Streams for Scala
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package fs2.protocols.ntp
+
+sealed trait LeapIndicator {
+  def value: Int = this match {
+    case LeapIndicator.NoAdjustment   => 0
+    case LeapIndicator.AddSecond      => 1
+    case LeapIndicator.SubtractSecond => 2
+    case LeapIndicator.Unsynchronized => 3
+  }
+}
+
+object LeapIndicator {
+  def from(value: Int): LeapIndicator = value match {
+    case 0 => LeapIndicator.NoAdjustment
+    case 1 => LeapIndicator.AddSecond
+    case 2 => LeapIndicator.SubtractSecond
+    case 3 => LeapIndicator.Unsynchronized
+  }
+  case object NoAdjustment extends LeapIndicator
+  case object AddSecond extends LeapIndicator
+  case object SubtractSecond extends LeapIndicator
+  case object Unsynchronized extends LeapIndicator
+}
diff --git a/protocols/shared/src/main/scala/fs2/protocols/ntp/NTPMode.scala b/protocols/shared/src/main/scala/fs2/protocols/ntp/NTPMode.scala
new file mode 100644
index 0000000000..1111da7293
--- /dev/null
+++ b/protocols/shared/src/main/scala/fs2/protocols/ntp/NTPMode.scala
@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2013 Functional Streams for Scala
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package fs2.protocols.ntp
+
+sealed trait NTPMode {
+  def value: Int = this match {
+    case NTPMode.Reserved         => 0
+    case NTPMode.SymmetricActive  => 1
+    case NTPMode.SymmetricPassive => 2
+    case NTPMode.Client           => 3
+    case NTPMode.Server           => 4
+    case NTPMode.Broadcast        => 5
+    case NTPMode.ControlMessage   => 6
+    case NTPMode.ReservedPrivate  => 7
+  }
+}
+object NTPMode {
+  case object Reserved extends NTPMode
+  case object SymmetricActive extends NTPMode
+  case object SymmetricPassive extends NTPMode
+  case object Client extends NTPMode
+  case object Server extends NTPMode
+
+  case object Broadcast extends NTPMode
+  case object ControlMessage extends NTPMode
+  case object ReservedPrivate extends NTPMode
+
+  def from(mode: Int): NTPMode = mode match {
+    case 0 => Reserved
+    case 1 => SymmetricActive
+    case 2 => SymmetricPassive
+    case 3 => Client
+    case 4 => Server
+    case 5 => Broadcast
+    case 6 => ControlMessage
+    case 7 => ReservedPrivate
+  }
+}
diff --git a/protocols/shared/src/main/scala/fs2/protocols/ntp/NTPPacket.scala b/protocols/shared/src/main/scala/fs2/protocols/ntp/NTPPacket.scala
new file mode 100644
index 0000000000..78c821bba3
--- /dev/null
+++ b/protocols/shared/src/main/scala/fs2/protocols/ntp/NTPPacket.scala
@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2013 Functional Streams for Scala
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package fs2.protocols.ntp
+
+import scodec.*
+import scodec.bits.*
+import scodec.codecs.*
+import org.typelevel.scalaccompat.annotation.*
+
+case class NTPPacket(
+    li: LeapIndicator,
+    version: Int,
+    mode: NTPMode,
+    stratum: Int,
+    poll: Int,
+    precision: Int,
+    rootDelay: Long,
+    rootDispersion: Long,
+    referenceID: Long,
+    referenceTime: BigInt,
+    originTime: BigInt,
+    receiveTime: BigInt,
+    transmitTime: BigInt
+)
+@nowarn3("msg=unused import")
+object NTPPacket extends NTPPacketCompat {
+  import scodec.compat.*
+
+  val default = NTPPacket(
+    li = LeapIndicator.NoAdjustment,
+    version = 3,
+    mode = NTPMode.Client,
+    stratum = 0,
+    poll = 0,
+    precision = 0x20,
+    rootDelay = 0,
+    rootDispersion = 0,
+    referenceID = 0,
+    referenceTime = 0,
+    originTime = 0,
+    receiveTime = 0,
+    transmitTime = 0
+  )
+
+  private[ntp] val ulong64: Codec[BigInt] = bytes(8)
+    .xmap(
+      _.toBigInt(false),
+      ByteVector.fromBigInt(_, Some(8))
+    )
+
+  private[ntp] val liVnMode: Codec[LeapIndicator *: Int *: NTPMode *: EmptyTuple] = uint8.xmap(
+    octet => {
+      val li = LeapIndicator.from(octet >> 6)
+      val version = (octet >> 3) & 0x07
+      val mode = NTPMode.from(octet & 0x07)
+      li *: version *: mode *: EmptyTuple
+    },
+    { case li *: version *: mode *: EmptyTuple =>
+      ((li.value & 0x3) << 6) | ((version & 0x07) << 3) | (mode.value & 0x07)
+    }
+  )
+
+  private[ntp] def layout =
+    ("li / version / mode" | liVnMode) ::
+      ("stratum" | uint8) ::
+      ("poll" | uint8) ::
+      ("precision" | uint8) ::
+      ("root delay" | uint32) ::
+      ("root dispersion" | uint32) ::
+      ("reference id" | uint32) ::
+      ("reference time" | ulong64) ::
+      ("origin time" | ulong64) ::
+      ("receive time" | ulong64) ::
+      ("transmit time" | ulong64)
+}
diff --git a/protocols/shared/src/test/scala/fs2/protocols/ntp/NTPPacketTest.scala b/protocols/shared/src/test/scala/fs2/protocols/ntp/NTPPacketTest.scala
new file mode 100644
index 0000000000..31a1f0c2fc
--- /dev/null
+++ b/protocols/shared/src/test/scala/fs2/protocols/ntp/NTPPacketTest.scala
@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2013 Functional Streams for Scala
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package fs2
+package protocols
+package ntp
+import org.scalacheck.Arbitrary
+import org.scalacheck.Gen
+import org.scalacheck.Prop
+import scodec.*
+import scodec.Attempt.Successful
+import scodec.bits.*
+import munit.Location
+import org.typelevel.scalaccompat.annotation.*
+
+@nowarn3("msg=unused import")
+class NTPPacketTest extends Fs2Suite {
+  import scodec.compat.*
+  import NTPPacketTestData._
+  test("ntp packet default roundtrip") {
+    roundtrip[NTPPacket](NTPPacket.codec, NTPPacket.default)
+  }
+
+  test("ulong64 roundtrip without long overflow") {
+    val Successful(encode) = NTPPacket.ulong64.encode(BigInt(Long.MaxValue) + 1): @unchecked
+    val Successful(decode) = NTPPacket.ulong64.decode(encode): @unchecked
+    assertEquals(decode.value, BigInt(Long.MaxValue) + 1)
+  }
+
+  test("arbitrary li vi mode roundtrip") {
+    Prop.forAll((tuple: LeapIndicator *: Int *: NTPMode *: EmptyTuple) =>
+      roundtrip(NTPPacket.liVnMode, tuple)
+    )
+  }
+
+  test("arbitrary ntp packet roundtrip") {
+    Prop.forAll((packet: NTPPacket) => roundtrip(NTPPacket.codec, packet))
+  }
+
+  private def roundtrip[A](codec: Codec[A], value: A)(implicit loc: Location): Unit = {
+    val Successful(encode) = codec.encode(value): @unchecked
+    val Successful(decode) = codec.decode(encode): @unchecked
+    assertEquals(decode.value, value)
+  }
+}
+
+@nowarn3("msg=unused import")
+object NTPPacketTestData {
+  import scodec.compat.*
+  lazy val genUInt8 = Gen.choose(0, 0xff)
+  lazy val genUInt32 = Gen.choose(0L, 0xffffffffL)
+  lazy val genULong64 = Gen.choose(BigInt(0), BigInt("18446744073709551615"))
+  lazy val genLeapIndicator = Gen.choose[Int](0, 3).map(LeapIndicator.from)
+  lazy val genNTPMode = Gen.choose[Int](0, 7).map(NTPMode.from)
+  lazy val genLiVnMode = for {
+    li <- genLeapIndicator
+    vn <- Gen.choose[Int](bin"001".toInt(false), bin"111".toInt(false))
+    mode <- genNTPMode
+  } yield li *: vn *: mode *: EmptyTuple
+  lazy val genNTPPacket = for {
+    liVnMode <- genLiVnMode
+    li *: vn *: mode *: EmptyTuple = liVnMode
+    stratum <- genUInt8
+    poll <- genUInt8
+    precision <- genUInt8
+    rootDelay <- genUInt32
+    rootDispersion <- genUInt32
+    referenceID <- genUInt32
+    referenceTime <- genULong64
+    originTime <- genULong64
+    receiveTime <- genULong64
+    transmitTime <- genULong64
+  } yield NTPPacket(
+    li,
+    vn,
+    mode,
+    stratum,
+    poll,
+    precision,
+    rootDelay,
+    rootDispersion,
+    referenceID,
+    referenceTime,
+    originTime,
+    receiveTime,
+    transmitTime
+  )
+  implicit val arbitraryLiVnMode: Arbitrary[LeapIndicator *: Int *: NTPMode *: EmptyTuple] =
+    Arbitrary(genLiVnMode)
+  implicit val arbitraryNTPPacket: Arbitrary[NTPPacket] = Arbitrary(genNTPPacket)
+}