Index: head/stand/i386/libi386/biosdisk.c
===================================================================
--- head/stand/i386/libi386/biosdisk.c
+++ head/stand/i386/libi386/biosdisk.c
@@ -882,6 +882,12 @@
 			}
 		}
 
+		if (alignlba + alignblks > BD(dev).bd_sectors) {
+			DEBUG("Shorted read at %llu from %d to %llu blocks",
+			    alignlba, alignblks, BD(dev).bd_sectors - alignlba);
+			alignblks = BD(dev).bd_sectors - alignlba;
+		}
+
 		err = bd_io(dev, alignlba, alignblks, tmpbuf, 0);
 		if (err)
 			return (err);
Index: head/stand/i386/zfsboot/zfsboot.c
===================================================================
--- head/stand/i386/zfsboot/zfsboot.c
+++ head/stand/i386/zfsboot/zfsboot.c
@@ -209,6 +209,12 @@
 		alignnb = roundup2(nb * DEV_BSIZE + diff, DEV_GELIBOOT_BSIZE)
 		    / DEV_BSIZE;
 
+		if (dsk->size > 0 && alignlba + alignnb > dsk->size + dsk->start) {
+			printf("Shortening read at %lld from %d to %lld\n", alignlba,
+			    alignnb, (dsk->size + dsk->start) - alignlba);
+			alignnb = (dsk->size + dsk->start) - alignlba;
+		}
+
 		if (drvread(dsk, dmadat->rdbuf, alignlba, alignnb))
 			return -1;
 #ifdef LOADER_GELI_SUPPORT
@@ -694,7 +700,7 @@
     dsk->slice = *(uint8_t *)PTOV(ARGS + 1) + 1;
     dsk->part = 0;
     dsk->start = 0;
-    dsk->size = 0;
+    dsk->size = drvsize_ext(dsk);
 
     bootinfo.bi_version = BOOTINFO_VERSION;
     bootinfo.bi_size = sizeof(bootinfo);
@@ -745,7 +751,7 @@
 	dsk->slice = 0;
 	dsk->part = 0;
 	dsk->start = 0;
-	dsk->size = 0;
+	dsk->size = drvsize_ext(dsk);
 	probe_drive(dsk);
     }