diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index f7918401a007..73c5f1f3d5d2 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -882,7 +882,7 @@ static u32 handle_block_output(int fd, const struct iovec *iov,
 		 * of the block file (possibly extending it). */
 		if (off + len > device_len) {
 			/* Trim it back to the correct length */
-			ftruncate(dev->fd, device_len);
+			ftruncate64(dev->fd, device_len);
 			/* Die, bad Guest, die. */
 			errx(1, "Write past end %llu+%u", off, len);
 		}