diff --git a/webrtc/modules/video_coding/packet_buffer.cc b/webrtc/modules/video_coding/packet_buffer.cc
index 7b01e4cb27..452e762b9f 100644
--- a/webrtc/modules/video_coding/packet_buffer.cc
+++ b/webrtc/modules/video_coding/packet_buffer.cc
@@ -40,7 +40,6 @@ PacketBuffer::PacketBuffer(Clock* clock,
       size_(start_buffer_size),
       max_size_(max_buffer_size),
       first_seq_num_(0),
-      last_seq_num_(0),
       first_packet_received_(false),
       is_cleared_to_first_seq_num_(false),
       data_buffer_(start_buffer_size),
@@ -65,7 +64,6 @@ bool PacketBuffer::InsertPacket(VCMPacket* packet) {
 
     if (!first_packet_received_) {
       first_seq_num_ = seq_num;
-      last_seq_num_ = seq_num;
       first_packet_received_ = true;
     } else if (AheadOf(first_seq_num_, seq_num)) {
       // If we have explicitly cleared past this packet then it's old,
@@ -100,9 +98,6 @@ bool PacketBuffer::InsertPacket(VCMPacket* packet) {
       }
     }
 
-    if (AheadOf(seq_num, last_seq_num_))
-      last_seq_num_ = seq_num;
-
     sequence_buffer_[index].frame_begin = packet->is_first_packet_in_frame;
     sequence_buffer_[index].frame_end = packet->markerBit;
     sequence_buffer_[index].seq_num = packet->seqNum;
@@ -186,6 +181,8 @@ bool PacketBuffer::PotentialNewFrame(uint16_t seq_num) const {
     return true;
   if (!sequence_buffer_[prev_index].used)
     return false;
+  if (sequence_buffer_[prev_index].frame_created)
+    return false;
   if (sequence_buffer_[prev_index].seq_num !=
       static_cast<uint16_t>(sequence_buffer_[index].seq_num - 1)) {
     return false;
diff --git a/webrtc/modules/video_coding/packet_buffer.h b/webrtc/modules/video_coding/packet_buffer.h
index da7e80ffaa..001f8bd89d 100644
--- a/webrtc/modules/video_coding/packet_buffer.h
+++ b/webrtc/modules/video_coding/packet_buffer.h
@@ -126,9 +126,6 @@ class PacketBuffer {
   // The fist sequence number currently in the buffer.
   uint16_t first_seq_num_ GUARDED_BY(crit_);
 
-  // The last sequence number currently in the buffer.
-  uint16_t last_seq_num_ GUARDED_BY(crit_);
-
   // If the packet buffer has received its first packet.
   bool first_packet_received_ GUARDED_BY(crit_);
 
diff --git a/webrtc/modules/video_coding/video_packet_buffer_unittest.cc b/webrtc/modules/video_coding/video_packet_buffer_unittest.cc
index ddb088c63e..d938b8b958 100644
--- a/webrtc/modules/video_coding/video_packet_buffer_unittest.cc
+++ b/webrtc/modules/video_coding/video_packet_buffer_unittest.cc
@@ -468,5 +468,14 @@ TEST_F(TestPacketBuffer, DontLeakPayloadData) {
   EXPECT_FALSE(Insert(2 + kMaxSize, kKeyFrame, kFirst, kNotLast, 5, data4));
 }
 
+TEST_F(TestPacketBuffer, ContinuousSeqNumDoubleMarkerBit) {
+  Insert(2, kKeyFrame, kNotFirst, kNotLast);
+  Insert(1, kKeyFrame, kFirst, kLast);
+  frames_from_callback_.clear();
+  Insert(3, kKeyFrame, kNotFirst, kLast);
+
+  EXPECT_EQ(0UL, frames_from_callback_.size());
+}
+
 }  // namespace video_coding
 }  // namespace webrtc
diff --git a/webrtc/test/fuzzers/BUILD.gn b/webrtc/test/fuzzers/BUILD.gn
index 141dcfe514..224b212c11 100644
--- a/webrtc/test/fuzzers/BUILD.gn
+++ b/webrtc/test/fuzzers/BUILD.gn
@@ -124,6 +124,16 @@ webrtc_fuzzer_test("flexfec_receiver_fuzzer") {
   libfuzzer_options = [ "max_len=2000" ]
 }
 
+webrtc_fuzzer_test("packet_buffer_fuzzer") {
+  sources = [
+    "packet_buffer_fuzzer.cc",
+  ]
+  deps = [
+    "../../modules/video_coding/",
+  ]
+  libfuzzer_options = [ "max_len=2000" ]
+}
+
 webrtc_fuzzer_test("rtcp_receiver_fuzzer") {
   sources = [
     "rtcp_receiver_fuzzer.cc",
diff --git a/webrtc/test/fuzzers/packet_buffer_fuzzer.cc b/webrtc/test/fuzzers/packet_buffer_fuzzer.cc
new file mode 100644
index 0000000000..099fe21fc2
--- /dev/null
+++ b/webrtc/test/fuzzers/packet_buffer_fuzzer.cc
@@ -0,0 +1,46 @@
+/*
+ *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/video_coding/packet_buffer.h"
+#include "webrtc/system_wrappers/include/clock.h"
+
+namespace webrtc {
+
+namespace {
+class NullCallback : public video_coding::OnReceivedFrameCallback {
+  void OnReceivedFrame(std::unique_ptr<video_coding::RtpFrameObject> frame) {}
+};
+}  // namespace
+
+void FuzzOneInput(const uint8_t* data, size_t size) {
+  // Two bytes for the sequence number,
+  // one byte for |is_first_packet_in_frame| and |markerBit|.
+  constexpr size_t kMinDataNeeded = 3;
+  if (size < kMinDataNeeded) {
+    return;
+  }
+
+  VCMPacket packet;
+  NullCallback callback;
+  SimulatedClock clock(0);
+  rtc::scoped_refptr<video_coding::PacketBuffer> packet_buffer(
+      video_coding::PacketBuffer::Create(&clock, 8, 1024, &callback));
+
+  size_t i = kMinDataNeeded;
+  while (i < size) {
+    memcpy(&packet.seqNum, &data[i - kMinDataNeeded], 2);
+    packet.is_first_packet_in_frame = data[i] & 1;
+    packet.markerBit = data[i] & 2;
+    packet_buffer->InsertPacket(&packet);
+    i += kMinDataNeeded;
+  }
+}
+
+}  // namespace webrtc