diff --git a/posix/spawn_faction_addopen.c b/posix/spawn_faction_addopen.c
index 40800b8..eba158c 100644
--- a/posix/spawn_faction_addopen.c
+++ b/posix/spawn_faction_addopen.c
@@ -18,6 +18,7 @@
 #include <errno.h>
 #include <spawn.h>
 #include <unistd.h>
+#include <string.h>
 
 #include "spawn_int.h"