diff --git a/src/lib9/lock.c b/src/lib9/lock.c
index e97b967f..80f65b33 100644
--- a/src/lib9/lock.c
+++ b/src/lib9/lock.c
@@ -1,5 +1,6 @@
 #include <u.h>
 #include <unistd.h>
+#include <sys/time.h>
 #include <sched.h>
 #include <libc.h>