diff --git a/timer.cpp b/timer.cpp
index a19351a..a6815c6 100644
--- a/timer.cpp
+++ b/timer.cpp
@@ -82,6 +82,8 @@ void Timer::addCallback(std::function<void ()> f, uint64_t interval_ms, const st
 {
     logger->logf(LOG_DEBUG, "Adding event '%s' to the timer with an interval of %ld ms.", name.c_str(), interval_ms);
 
+    std::lock_guard<std::mutex> locker(this->callbacksMutex);
+
     CallbackEntry c;
     c.f = f;
     c.interval = interval_ms;
@@ -137,6 +139,9 @@ void Timer::process()
         }
 
         logger->logf(LOG_DEBUG, "Calling timed event '%s'.", callbacks.front().name.c_str());
+
+        std::lock_guard<std::mutex> locker(this->callbacksMutex);
+
         CallbackEntry &c = callbacks.front();
         c.updateExectedAt();
         c.f();
diff --git a/timer.h b/timer.h
index 1567d58..6aae4c2 100644
--- a/timer.h
+++ b/timer.h
@@ -50,6 +50,7 @@ class Timer
     int running = false;
     Logger *logger = Logger::getInstance();
     std::vector<CallbackEntry> callbacks;
+    std::mutex callbacksMutex;
 
     void sortAndSetSleeptimeTillNext();
     void process();