diff --git a/sunshine/thread_safe.h b/sunshine/thread_safe.h
index b10089e3..c593fcff 100644
--- a/sunshine/thread_safe.h
+++ b/sunshine/thread_safe.h
@@ -9,6 +9,7 @@
 #include <mutex>
 #include <condition_variable>
 #include <atomic>
+#include <functional>
 
 #include "utility.h"