diff --git a/user/usertests.c b/user/usertests.c
index a809516..5e6e4dc 100644
--- a/user/usertests.c
+++ b/user/usertests.c
@@ -239,7 +239,7 @@ copyinstr3(char *s)
 // See if the kernel refuses to read/write user memory that the
 // application doesn't have anymore, because it returned it.
 void
-rwsbrk()
+rwsbrk(char *unused)
 {
   int fd, n;