diff --git a/remoting/protocol/webrtc_event_log_data.cc b/remoting/protocol/webrtc_event_log_data.cc
index 322e277359329d..2525eb4ce4cb80 100644
--- a/remoting/protocol/webrtc_event_log_data.cc
+++ b/remoting/protocol/webrtc_event_log_data.cc
@@ -12,6 +12,7 @@
 namespace remoting::protocol {
 
 WebrtcEventLogData::WebrtcEventLogData() {
+  base::AutoLock auto_lock(lock_);
   // See the caveat for base::circular_deque::reserve(). Calling reserve() is
   // OK here, since items are never removed until the list reaches its maximum
   // allowed size.
@@ -25,17 +26,20 @@ void WebrtcEventLogData::SetMaxSectionSizeForTest(int max_section_size) {
 }
 
 void WebrtcEventLogData::SetMaxSectionsForTest(int max_sections) {
+  base::AutoLock auto_lock(lock_);
   max_sections_ = max_sections;
   sections_.reserve(max_sections_);
 }
 
 base::circular_deque<WebrtcEventLogData::LogSection>
 WebrtcEventLogData::TakeLogData() {
+  base::AutoLock auto_lock(lock_);
   auto result = std::move(sections_);
 
-  // The |sections_| container is still valid but unspecified. Call Clear() to
-  // be certain it is empty (and the correct capacity is reserved).
-  Clear();
+  // The |sections_| container is still valid but unspecified. Clear it and
+  // reserve the correct capacity.
+  sections_.clear();
+  sections_.reserve(max_sections_);
   return result;
 }
 
@@ -44,6 +48,7 @@ void WebrtcEventLogData::Write(std::string_view log_event) {
     LOG(WARNING) << "Oversized RTC log event: size = " << log_event.size();
   }
 
+  base::AutoLock auto_lock(lock_);
   if (NeedNewSection(log_event.size())) {
     CreateNewSection();
   }
@@ -54,6 +59,7 @@ void WebrtcEventLogData::Write(std::string_view log_event) {
 }
 
 void WebrtcEventLogData::Clear() {
+  base::AutoLock auto_lock(lock_);
   sections_.clear();
   sections_.reserve(max_sections_);
 }
diff --git a/remoting/protocol/webrtc_event_log_data.h b/remoting/protocol/webrtc_event_log_data.h
index 53e2b9ddf0587e..a9e26818a44ed9 100644
--- a/remoting/protocol/webrtc_event_log_data.h
+++ b/remoting/protocol/webrtc_event_log_data.h
@@ -10,6 +10,8 @@
 #include <vector>
 
 #include "base/containers/circular_deque.h"
+#include "base/synchronization/lock.h"
+#include "base/thread_annotations.h"
 
 namespace remoting::protocol {
 
@@ -50,14 +52,19 @@ class WebrtcEventLogData {
 
  private:
   // Returns true if a new section must be created to store the event.
-  bool NeedNewSection(size_t log_event_size) const;
+  bool NeedNewSection(size_t log_event_size) const
+      EXCLUSIVE_LOCKS_REQUIRED(lock_);
 
   // Appends a new section of zero size to the end of the list, removing the
   // oldest one if necessary. On return, the section at the end (the list's
   // "back") will be empty, ready to accept the new data.
-  void CreateNewSection();
+  void CreateNewSection() EXCLUSIVE_LOCKS_REQUIRED(lock_);
 
-  base::circular_deque<LogSection> sections_;
+  // Write() is called on the WebRTC "rtc_event_log" task queue (a
+  // base::ThreadPool sequence in Chromium), while TakeLogData() is called on
+  // the CRD network thread. |lock_| serializes access to |sections_|.
+  mutable base::Lock lock_;
+  base::circular_deque<LogSection> sections_ GUARDED_BY(lock_);
 
   // Value chosen to keep the memory-usage within reasonable limits, but also
   // allow for recording "most" sessions entirely.