diff --git a/src/unistd/dup3.c b/src/unistd/dup3.c
index f919f791..1e7dc3e7 100644
--- a/src/unistd/dup3.c
+++ b/src/unistd/dup3.c
@@ -9,9 +9,10 @@ int __dup3(int old, int new, int flags)
 	int r;
 #ifdef SYS_dup2
 	if (old==new) return __syscall_ret(-EINVAL);
-	if (flags & O_CLOEXEC) {
+	if (flags) {
 		while ((r=__syscall(SYS_dup3, old, new, flags))==-EBUSY);
 		if (r!=-ENOSYS) return __syscall_ret(r);
+		if (flags & ~O_CLOEXEC) return __syscall_ret(-EINVAL);
 	}
 	while ((r=__syscall(SYS_dup2, old, new))==-EBUSY);
 	if (flags & O_CLOEXEC) __syscall(SYS_fcntl, new, F_SETFD, FD_CLOEXEC);