diff --git a/test/fixtures/fixture_log_observer.cpp b/test/fixtures/fixture_log_observer.cpp
index f28bbdcd2..a6e89e2e7 100644
--- a/test/fixtures/fixture_log_observer.cpp
+++ b/test/fixtures/fixture_log_observer.cpp
@@ -31,16 +31,22 @@ bool FixtureLog::Observer::onRecord(EventSeverity severity,
                                     Event event,
                                     int64_t code,
                                     const std::string& msg) {
+    std::lock_guard<std::mutex> lock(messagesMutex);
+
     messages.emplace_back(severity, event, code, msg);
 
     return true;
 }
 
 bool FixtureLog::Observer::empty() const {
+    std::lock_guard<std::mutex> lock(messagesMutex);
+
     return messages.empty();
 }
 
 size_t FixtureLog::Observer::count(const Message& message) const {
+    std::lock_guard<std::mutex> lock(messagesMutex);
+
     size_t message_count = 0;
     for (const auto& msg : messages) {
         if (msg == message) {
@@ -70,6 +76,8 @@ FixtureLog::~FixtureLog() {
 }
 
 std::vector<FixtureLog::Message> FixtureLogObserver::unchecked() const {
+    std::lock_guard<std::mutex> lock(messagesMutex);
+
     std::vector<Message> unchecked_messages;
     for (const auto& msg : messages) {
         if (!msg.checked) {
diff --git a/test/fixtures/fixture_log_observer.hpp b/test/fixtures/fixture_log_observer.hpp
index f28bb552a..f2ccb5cb5 100644
--- a/test/fixtures/fixture_log_observer.hpp
+++ b/test/fixtures/fixture_log_observer.hpp
@@ -5,6 +5,7 @@
 
 #include <vector>
 #include <cstdarg>
+#include <mutex>
 #include <iostream>
 
 namespace mbgl {
@@ -42,9 +43,10 @@ public:
         size_t count(const Message& message) const;
         std::vector<Message> unchecked() const;
 
-    public:
+    private:
         FixtureLog* log;
         std::vector<Message> messages;
+        mutable std::mutex messagesMutex;
     };
 
     FixtureLog();