diff --git a/fio.1 b/fio.1
index 2eb4455..dd8eda9 100644
--- a/fio.1
+++ b/fio.1
@@ -193,6 +193,12 @@
 If set, any size in \fBblocksize_range\fR may be used.  This typically won't
 work with direct I/O, as that normally requires sector alignment.
 .TP
+.BI blockalign \fR=\fPint[,int] "\fR,\fB ba" \fR=\fPint[,int]
+At what boundary to align random IO offsets. Defaults to the same as
+'blocksize' the minimum blocksize given.  Minimum alignment is typically 512b
+for using direct IO, though it usually depends on the hardware block size.
+This option is mutually exclusive with using a random map for files, so it
+will turn off that option.
 .B zero_buffers
 Initialise buffers with all zeros. Default: fill buffers with random data.
 .TP