diff --git a/src/threads/winlocks.c b/src/threads/winlocks.c
index a1799531..da600418 100644
--- a/src/threads/winlocks.c
+++ b/src/threads/winlocks.c
@@ -26,6 +26,7 @@
 #include <windows.h>
 #include <winbase.h>
 #include <errno.h>
+#include <stdlib.h>
 
 static int ssh_winlock_mutex_init (void **priv)
 {