diff --git a/pc/rtc_stats_collector.cc b/pc/rtc_stats_collector.cc
index e4a541805a..f0070dfda6 100644
--- a/pc/rtc_stats_collector.cc
+++ b/pc/rtc_stats_collector.cc
@@ -815,9 +815,11 @@ ProduceRemoteInboundRtpStreamStatsFromReportBlockData(
   remote_inbound->packets_lost = report_block.packets_lost;
   remote_inbound->fraction_lost =
       static_cast<double>(report_block.fraction_lost) / (1 << 8);
-  remote_inbound->round_trip_time =
-      static_cast<double>(report_block_data.last_rtt_ms()) /
-      rtc::kNumMillisecsPerSec;
+  if (report_block_data.num_rtts() > 0) {
+    remote_inbound->round_trip_time =
+        static_cast<double>(report_block_data.last_rtt_ms()) /
+        rtc::kNumMillisecsPerSec;
+  }
   remote_inbound->total_round_trip_time =
       static_cast<double>(report_block_data.sum_rtt_ms()) /
       rtc::kNumMillisecsPerSec;
diff --git a/pc/rtc_stats_collector_unittest.cc b/pc/rtc_stats_collector_unittest.cc
index a3a17801c1..1982446667 100644
--- a/pc/rtc_stats_collector_unittest.cc
+++ b/pc/rtc_stats_collector_unittest.cc
@@ -3557,6 +3557,32 @@ TEST_P(RTCStatsCollectorTestWithParamKind,
   }
 }
 
+TEST_P(RTCStatsCollectorTestWithParamKind,
+       RTCRemoteInboundRtpStreamStatsRttMissingBeforeMeasurement) {
+  constexpr int64_t kReportBlockTimestampUtcUs = 123456789;
+
+  RTCPReportBlock report_block;
+  // The remote-inbound-rtp SSRC and the outbound-rtp SSRC is the same as the
+  // `source_ssrc`, "SSRC of the RTP packet sender".
+  report_block.source_ssrc = 12;
+  ReportBlockData report_block_data;  // AddRoundTripTimeSample() not called.
+  report_block_data.SetReportBlock(report_block, kReportBlockTimestampUtcUs);
+
+  AddSenderInfoAndMediaChannel("TransportName", {report_block_data},
+                               absl::nullopt);
+
+  rtc::scoped_refptr<const RTCStatsReport> report = stats_->GetStatsReport();
+
+  std::string remote_inbound_rtp_id = "RI" + MediaTypeCharStr() + "12";
+  ASSERT_TRUE(report->Get(remote_inbound_rtp_id));
+  auto& remote_inbound_rtp = report->Get(remote_inbound_rtp_id)
+                                 ->cast_to<RTCRemoteInboundRtpStreamStats>();
+
+  EXPECT_TRUE(remote_inbound_rtp.round_trip_time_measurements.is_defined());
+  EXPECT_EQ(0, *remote_inbound_rtp.round_trip_time_measurements);
+  EXPECT_FALSE(remote_inbound_rtp.round_trip_time.is_defined());
+}
+
 TEST_P(RTCStatsCollectorTestWithParamKind,
        RTCRemoteInboundRtpStreamStatsWithTimestampFromReportBlock) {
   const int64_t kReportBlockTimestampUtcUs = 123456789;