diff --git a/modules/rtp_rtcp/source/rtcp_packet/report_block.cc b/modules/rtp_rtcp/source/rtcp_packet/report_block.cc
index 4f98963766..d4579fc8d6 100644
--- a/modules/rtp_rtcp/source/rtcp_packet/report_block.cc
+++ b/modules/rtp_rtcp/source/rtcp_packet/report_block.cc
@@ -54,7 +54,7 @@ bool ReportBlock::Parse(const uint8_t* buffer, size_t length) {
 
   source_ssrc_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[0]);
   fraction_lost_ = buffer[4];
-  cumulative_lost_ = ByteReader<uint32_t, 3>::ReadBigEndian(&buffer[5]);
+  cumulative_lost_ = ByteReader<int32_t, 3>::ReadBigEndian(&buffer[5]);
   extended_high_seq_num_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[8]);
   jitter_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[12]);
   last_sr_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[16]);
diff --git a/modules/rtp_rtcp/source/rtcp_packet/report_block_unittest.cc b/modules/rtp_rtcp/source/rtcp_packet/report_block_unittest.cc
index a074a2f4f4..5cc102fed0 100644
--- a/modules/rtp_rtcp/source/rtcp_packet/report_block_unittest.cc
+++ b/modules/rtp_rtcp/source/rtcp_packet/report_block_unittest.cc
@@ -91,5 +91,20 @@ TEST(RtcpPacketReportBlockTest, ValidateCumulativeLost) {
   EXPECT_EQ(0u, rb.cumulative_lost());
 }
 
+TEST(RtcpPacketReportBlockTest, ParseNegativeCumulativeLost) {
+  // CumulativeLost is a signed 24-bit integer.
+  const int32_t kNegativeCumulativeLost = -123;
+  ReportBlock rb;
+  EXPECT_TRUE(rb.SetCumulativeLost(kNegativeCumulativeLost));
+
+  uint8_t buffer[kBufferLength];
+  rb.Create(buffer);
+
+  ReportBlock parsed;
+  EXPECT_TRUE(parsed.Parse(buffer, kBufferLength));
+
+  EXPECT_EQ(kNegativeCumulativeLost, parsed.cumulative_lost_signed());
+}
+
 }  // namespace
 }  // namespace webrtc