diff --git a/faiss/utils/WorkerThread.h b/faiss/utils/WorkerThread.h
index 72529be0a3..3f2377eba2 100644
--- a/faiss/utils/WorkerThread.h
+++ b/faiss/utils/WorkerThread.h
@@ -9,6 +9,7 @@
 
 #include <condition_variable>
 #include <deque>
+#include <functional>
 #include <future>
 #include <thread>