diff --git a/quic/QuicConstants.h b/quic/QuicConstants.h
index 7792e3829..aa9a44197 100644
--- a/quic/QuicConstants.h
+++ b/quic/QuicConstants.h
@@ -487,6 +487,9 @@ constexpr TransportPartialReliabilitySetting kDefaultPartialReliability = false;
 
 constexpr uint64_t kMaxPacketNumber = (1ull << 62) - 1;
 
+// Use up to 3 bytes for the initial packet number.
+constexpr uint32_t kMaxInitialPacketNum = 0xffffff;
+
 enum class ZeroRttSourceTokenMatchingPolicy : uint8_t {
   REJECT_IF_NO_EXACT_MATCH = 0,
   LIMIT_IF_NO_EXACT_MATCH = 1,
diff --git a/quic/api/test/QuicPacketSchedulerTest.cpp b/quic/api/test/QuicPacketSchedulerTest.cpp
index 4ee78b00d..56e6a0063 100644
--- a/quic/api/test/QuicPacketSchedulerTest.cpp
+++ b/quic/api/test/QuicPacketSchedulerTest.cpp
@@ -344,7 +344,8 @@ TEST_F(QuicPacketSchedulerTest, CryptoWritePartialLossBuffer) {
   RegularQuicPacketBuilder builder(
       25,
       std::move(longHeader),
-      conn.ackStates.initialAckState.largestAckedByPeer.value_or(0));
+      conn.ackStates.initialAckState.largestAckedByPeer.value_or(
+          conn.ackStates.initialAckState.nextPacketNum));
   FrameScheduler cryptoOnlyScheduler =
       std::move(
           FrameScheduler::Builder(
diff --git a/quic/codec/PacketNumber.cpp b/quic/codec/PacketNumber.cpp
index 8e5c85faf..811f3605b 100644
--- a/quic/codec/PacketNumber.cpp
+++ b/quic/codec/PacketNumber.cpp
@@ -18,9 +18,6 @@ PacketNumEncodingResult::PacketNumEncodingResult(
 PacketNumEncodingResult encodePacketNumber(
     PacketNum packetNum,
     PacketNum largestAckedPacketNum) {
-  DCHECK(
-      (!packetNum && !largestAckedPacketNum) ||
-      packetNum > largestAckedPacketNum);
   PacketNum twiceDistance = (packetNum - largestAckedPacketNum) * 2;
   // The number of bits we need to mask all set bits in twiceDistance.
   // This is 1 + floor(log2(x)).
diff --git a/quic/common/test/TestUtils.cpp b/quic/common/test/TestUtils.cpp
index b07d5d4ec..de438f4b7 100644
--- a/quic/common/test/TestUtils.cpp
+++ b/quic/common/test/TestUtils.cpp
@@ -121,7 +121,7 @@ RegularQuicPacketBuilder::Packet createAckPacket(
   RegularQuicPacketBuilder builder(
       dstConn.udpSendPacketLen,
       std::move(*header),
-      getAckState(dstConn, pnSpace).largestAckedByPeer.value_or(0));
+      getAckState(dstConn, pnSpace).largestAckScheduled.value_or(0));
   builder.encodePacketHeader();
   if (aead) {
     builder.accountForCipherOverhead(aead->getCipherOverhead());
diff --git a/quic/state/AckStates.h b/quic/state/AckStates.h
index b3b59feca..e490663e4 100644
--- a/quic/state/AckStates.h
+++ b/quic/state/AckStates.h
@@ -8,9 +8,12 @@
 
 #pragma once
 
+#include <quic/QuicConstants.h>
 #include <quic/codec/Types.h>
 #include <quic/common/IntervalSet.h>
 
+#include <folly/Random.h>
+
 namespace quic {
 
 // Ack and PacketNumber states. This is per-packet number space.
@@ -41,6 +44,13 @@ struct AckState {
 };
 
 struct AckStates {
+  AckStates() {
+    PacketNum randomizedPacketNum =
+        folly::Random::secureRand32(kMaxInitialPacketNum);
+    initialAckState.nextPacketNum = randomizedPacketNum;
+    handshakeAckState.nextPacketNum = randomizedPacketNum;
+    appDataAckState.nextPacketNum = randomizedPacketNum;
+  }
   // AckState for acks to peer packets in Initial packet number space.
   AckState initialAckState;
   // AckState for acks to peer packets in Handshake packet number space.