diff --git a/rtc_base/logging.cc b/rtc_base/logging.cc
index 798c059fb3..4bc9183d97 100644
--- a/rtc_base/logging.cc
+++ b/rtc_base/logging.cc
@@ -138,9 +138,10 @@ LogMessage::LogMessage(const char* file,
                        int err) {
   log_line_.set_severity(sev);
   if (log_timestamp_) {
+    int64_t log_start_time = LogStartTime();
     // Use SystemTimeMillis so that even if tests use fake clocks, the timestamp
     // in log messages represents the real system time.
-    int64_t time = TimeDiff(SystemTimeMillis(), LogStartTime());
+    int64_t time = TimeDiff(SystemTimeMillis(), log_start_time);
     // Also ensure WallClockStartTime is initialized, so that it matches
     // LogStartTime.
     WallClockStartTime();