Index: sys/aio/aio_test.c
===================================================================
--- sys/aio/aio_test.c
+++ sys/aio/aio_test.c
@@ -794,7 +794,7 @@
 	mdio.md_version = MDIOVERSION;
 	mdio.md_type = MD_MALLOC;
 	mdio.md_options = MD_AUTOUNIT | MD_COMPRESS;
-	mdio.md_mediasize = GLOBAL_MAX;
+	mdio.md_mediasize = 1024 * 1024;  /* 1 MB for max_buf_aio up to 2047 */
 	mdio.md_sectorsize = 512;
 	strlcpy(buf, __func__, sizeof(buf));
 	mdio.md_label = buf;
@@ -1846,7 +1846,9 @@
 		atf_tc_fail("aio failed: %s", strerror(errno));
 
 	if (len != buflen)
-		atf_tc_fail("aio short write (%jd)", (intmax_t)len);
+		atf_tc_fail("aio short write: got %jd, expected: %jd "
+			"(max_buf_aio=%d, iovcnt=%zu)",
+			(intmax_t)len, (intmax_t)buflen, max_buf_aio, aio.aio_iovcnt);
 
 	bzero(&aio, sizeof(aio));
 	aio.aio_fildes = fd;