diff --git a/src/sled/timer/timer.h b/src/sled/timer/timer.h
index 462f74f..9108f36 100644
--- a/src/sled/timer/timer.h
+++ b/src/sled/timer/timer.h
@@ -3,6 +3,7 @@
 #define SLED_TIMER_TIMER_H
 
 #include "timeout.h"
+#include <atomic>
 #include <map>
 #include <memory>
 #include <sled/optional.h>