diff --git a/quic/core/quic_sent_packet_manager.cc b/quic/core/quic_sent_packet_manager.cc
index f0ee1a7..512632d 100644
--- a/quic/core/quic_sent_packet_manager.cc
+++ b/quic/core/quic_sent_packet_manager.cc
@@ -844,8 +844,9 @@
     // Find out the packet number space to send probe packets.
     if (!GetEarliestPacketSentTimeForPto(&packet_number_space)
              .IsInitialized()) {
-      QUIC_BUG << "earlist_sent_time not initialized when trying to send PTO "
-                  "retransmissions";
+      QUIC_BUG_IF(unacked_packets_.perspective() == Perspective::IS_SERVER)
+          << "earlist_sent_time not initialized when trying to send PTO "
+             "retransmissions";
       return;
     }
   }
@@ -1067,8 +1068,12 @@
       PacketNumberSpace packet_number_space = NUM_PACKET_NUMBER_SPACES;
       // earliest_right_edge is the earliest sent time of the last in flight
       // packet of all packet number spaces.
-      const QuicTime earliest_right_edge =
+      QuicTime earliest_right_edge =
           GetEarliestPacketSentTimeForPto(&packet_number_space);
+      if (!earliest_right_edge.IsInitialized()) {
+        // Arm PTO from now if there is no in flight packets.
+        earliest_right_edge = clock_->ApproximateNow();
+      }
       if (first_pto_srtt_multiplier_ > 0 &&
           packet_number_space == APPLICATION_DATA &&
           consecutive_pto_count_ == 0) {
diff --git a/quic/core/quic_sent_packet_manager_test.cc b/quic/core/quic_sent_packet_manager_test.cc
index 7efa8e3..9d62bb6 100644
--- a/quic/core/quic_sent_packet_manager_test.cc
+++ b/quic/core/quic_sent_packet_manager_test.cc
@@ -3825,6 +3825,37 @@
             manager_.GetRetransmissionTime());
 }
 
+TEST_F(QuicSentPacketManagerTest, HandshakeAckCausesInitialKeyDropping) {
+  manager_.EnableMultiplePacketNumberSpacesSupport();
+  QuicSentPacketManagerPeer::SetPerspective(&manager_, Perspective::IS_CLIENT);
+  // Send INITIAL packet 1.
+  SendDataPacket(1, ENCRYPTION_INITIAL);
+  QuicTime::Delta expected_pto_delay =
+      QuicTime::Delta::FromMilliseconds(3 * kInitialRttMs);
+  EXPECT_EQ(clock_.Now() + expected_pto_delay,
+            manager_.GetRetransmissionTime());
+  // Send HANDSHAKE ack.
+  clock_.AdvanceTime(QuicTime::Delta::FromMilliseconds(10));
+  SendAckPacket(2, /*largest_acked=*/1, ENCRYPTION_HANDSHAKE);
+  // Sending HANDSHAKE packet causes dropping of INITIAL key.
+  EXPECT_CALL(notifier_, HasUnackedCryptoData()).WillRepeatedly(Return(false));
+  EXPECT_CALL(notifier_, IsFrameOutstanding(_)).WillRepeatedly(Return(false));
+  manager_.NeuterUnencryptedPackets();
+  // There is no in flight packets.
+  EXPECT_FALSE(manager_.HasInFlightPackets());
+  // Verify PTO timer gets rearmed from now because of anti-amplification.
+  EXPECT_EQ(clock_.Now() + expected_pto_delay,
+            manager_.GetRetransmissionTime());
+
+  // Invoke PTO.
+  clock_.AdvanceTime(expected_pto_delay);
+  manager_.OnRetransmissionTimeout();
+  // Verify nothing to probe (and connection will send PING for current
+  // encryption level).
+  EXPECT_CALL(notifier_, RetransmitFrames(_, _)).Times(0);
+  manager_.MaybeSendProbePackets();
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace quic