diff --git a/src/sound/oalsound.cpp b/src/sound/oalsound.cpp
index e9fde9263..6ee152cfd 100644
--- a/src/sound/oalsound.cpp
+++ b/src/sound/oalsound.cpp
@@ -39,6 +39,7 @@
 #include <dlfcn.h>
 #endif
 
+#include <functional>
 #include <memory>
 #include <chrono>