Index: head/stand/efi/libefi/efipart.c
===================================================================
--- head/stand/efi/libefi/efipart.c
+++ head/stand/efi/libefi/efipart.c
@@ -257,6 +257,14 @@
 		    !blkio->Media->MediaPresent) {
 			return (false);
 		}
+
+		/*
+		 * We assume the block size 512 or greater power of 2. 
+		 */
+		if (blkio->Media->BlockSize < 512 ||
+		    !powerof2(blkio->Media->BlockSize)) {
+			return (false);
+		}
 	}
 	return (true);
 }