diff --git a/config.h b/config.h
index f06992a2..be6eda31 100644
--- a/config.h
+++ b/config.h
@@ -814,6 +814,7 @@ NAMESPACE_END
 #endif
 
 #ifdef CRYPTOPP_WIN32_AVAILABLE
+#include <winapifamily.h>
 # if !defined(WINAPI_FAMILY)
 #	define THREAD_TIMER_AVAILABLE
 # elif defined(WINAPI_FAMILY)