diff --git a/headless/load_session.cc b/headless/load_session.cc
index 68940617ea..c19b6c32f9 100644
--- a/headless/load_session.cc
+++ b/headless/load_session.cc
@@ -21,6 +21,7 @@ using namespace ARDOUR;
 using namespace PBD;
 
 #ifdef PLATFORM_WINDOWS
+#include <windows.h>
 #define sleep(X) Sleep((X) * 1000)
 #endif