--- dd.c	2013-12-21 21:07:38.000000000 +0800
+++ dd.c	2013-12-21 21:57:32.000000000 +0800
@@ -49,6 +49,7 @@ 
 #include <sys/stat.h>
 #include <sys/conf.h>
 #include <sys/disklabel.h>
+#include <sys/disk.h>
 #include <sys/filio.h>
 #include <sys/time.h>
 
@@ -469,6 +470,17 @@ 
 			if (nw <= 0) {
 				if (nw == 0)
 					errx(1, "%s: end of device", out.name);
+				if (errno == EINVAL){
+					size_t sectorsz = 0;
+					if (ioctl(out.fd, DIOCGSECTORSIZE , &sectorsz) == 0) { 
+						if ( out.dbsz % sectorsz)
+							errx(1, "bs=%zu: not a multiple of %s's sector size (%zu bytes)",
+									out.dbsz, out.name, sectorsz);
+						else if (cnt < sectorsz)
+							errx(1, "%s: not a multiple of %s's sector size (%zu bytes)",
+									in.name, out.name, sectorsz);
+					}
+				}
 				if (errno != EINTR)
 					err(1, "%s", out.name);
 				nw = 0;