diff --git a/man2/open.2 b/man2/open.2
index 389945f..c80686d 100644
--- a/man2/open.2
+++ b/man2/open.2
@@ -1322,7 +1322,16 @@ operation in
 Under Linux 2.4, transfer sizes, and the alignment of the user buffer
 and the file offset must all be multiples of the logical block size
 of the filesystem.
-Under Linux 2.6, alignment to 512-byte boundaries suffices.
+Under Linux 2.6 and newer, alignment to the logical block size of the
+underlying storage (typically 512 bytes) suffices.
+Logical block size can be determined with
+.BR ioctl (2)
+.B BLKSSZGET
+system call or
+.BR blockdev (8)
+command with
+.B --getss
+parameter.
 .LP
 .B O_DIRECT
 I/Os should never be run concurrently with the