diff --git a/quic/core/congestion_control/bandwidth_sampler.cc b/quic/core/congestion_control/bandwidth_sampler.cc
index 6eacef3..ee6d6c1 100644
--- a/quic/core/congestion_control/bandwidth_sampler.cc
+++ b/quic/core/congestion_control/bandwidth_sampler.cc
@@ -174,9 +174,12 @@
                << max_tracked_packets_
                << ").  First tracked: " << connection_state_map_.first_packet()
                << "; last tracked: " << connection_state_map_.last_packet()
-               << "; least unacked: " << unacked_packet_map_->GetLeastUnacked()
-               << "; packet number: " << packet_number << "; largest observed: "
-               << unacked_packet_map_->largest_acked();
+               << "; entry_slots_used: "
+               << connection_state_map_.entry_slots_used()
+               << "; number_of_present_entries: "
+               << connection_state_map_.number_of_present_entries()
+               << "; packet number: " << packet_number
+               << "; unacked_map: " << unacked_packet_map_->DebugString();
     } else {
       QUIC_BUG << "BandwidthSampler in-flight packet map has exceeded maximum "
                   "number of tracked packets.";
diff --git a/quic/core/quic_unacked_packet_map.h b/quic/core/quic_unacked_packet_map.h
index 4541351..2e5a64e 100644
--- a/quic/core/quic_unacked_packet_map.h
+++ b/quic/core/quic_unacked_packet_map.h
@@ -15,6 +15,7 @@
 #include "net/third_party/quiche/src/quic/core/session_notifier_interface.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_export.h"
 #include "net/third_party/quiche/src/quic/platform/api/quic_flags.h"
+#include "net/third_party/quiche/src/common/platform/api/quiche_str_cat.h"
 
 namespace quic {
 
@@ -318,6 +319,16 @@
     }
   }
 
+  std::string DebugString() const {
+    return quiche::QuicheStringPrintf(
+        "{size: %zu, least_unacked: %s, largest_sent_packet: %s, "
+        "largest_acked: %s, bytes_in_flight: %zu, packets_in_flight: %zu}",
+        unacked_packets_size(), least_unacked_.ToString().c_str(),
+        largest_sent_packet_.ToString().c_str(),
+        largest_acked_.ToString().c_str(), bytes_in_flight_,
+        packets_in_flight_);
+  }
+
  private:
   friend class test::QuicUnackedPacketMapPeer;
 
diff --git a/quic/core/quic_unacked_packet_map_test.cc b/quic/core/quic_unacked_packet_map_test.cc
index 0282108..4b598be 100644
--- a/quic/core/quic_unacked_packet_map_test.cc
+++ b/quic/core/quic_unacked_packet_map_test.cc
@@ -669,6 +669,32 @@
   ASSERT_EQ(QuicUnackedPacketMapPeer::GetCapacity(unacked_packets), 16u);
 }
 
+TEST_P(QuicUnackedPacketMapTest, DebugString) {
+  EXPECT_EQ(unacked_packets_.DebugString(),
+            "{size: 0, least_unacked: 1, largest_sent_packet: uninitialized, "
+            "largest_acked: uninitialized, bytes_in_flight: 0, "
+            "packets_in_flight: 0}");
+
+  SerializedPacket packet1(CreateRetransmittablePacket(1));
+  unacked_packets_.AddSentPacket(&packet1, NOT_RETRANSMISSION, now_, true,
+                                 true);
+  EXPECT_EQ(
+      unacked_packets_.DebugString(),
+      "{size: 1, least_unacked: 1, largest_sent_packet: 1, largest_acked: "
+      "uninitialized, bytes_in_flight: 1000, packets_in_flight: 1}");
+
+  SerializedPacket packet2(CreateRetransmittablePacket(2));
+  unacked_packets_.AddSentPacket(&packet2, NOT_RETRANSMISSION, now_, true,
+                                 true);
+  unacked_packets_.RemoveFromInFlight(QuicPacketNumber(1));
+  unacked_packets_.IncreaseLargestAcked(QuicPacketNumber(1));
+  unacked_packets_.RemoveObsoletePackets();
+  EXPECT_EQ(
+      unacked_packets_.DebugString(),
+      "{size: 1, least_unacked: 2, largest_sent_packet: 2, largest_acked: 1, "
+      "bytes_in_flight: 1000, packets_in_flight: 1}");
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace quic