diff --git a/cmd/ztest/ztest.c b/cmd/ztest/ztest.c
index b4c288df1d..6ee208361e 100644
--- a/cmd/ztest/ztest.c
+++ b/cmd/ztest/ztest.c
@@ -1162,7 +1162,7 @@ grow_vdev(vdev_t *vd, void *arg)
 		return (vd);
 
 	fsize = lseek(fd, 0, SEEK_END);
-	(void) ftruncate(fd, *newsize);
+	VERIFY(ftruncate(fd, *newsize) == 0);
 
 	if (zopt_verbose >= 6) {
 		(void) printf("%s grew from %lu to %lu bytes\n",