diff --git a/rdfind.1 b/rdfind.1
index 7f60c3b..4528561 100644
--- a/rdfind.1
+++ b/rdfind.1
@@ -80,6 +80,11 @@ is true.
 What type of checksum to be used: md5, sha1, sha256 or sha512. The default is
 sha1 since version 1.4.0.
 .TP
+.BR \-buffersize " " \fIN\fR " " (N=4096,0<N<1000KB)
+Chunksize when calculating the checksum
+for files, smaller or bigger can improve performance
+dependent on filesystem and checksum algorithm.
+.TP
 .BR \-deterministic " " \fItrue\fR|\fIfalse\fR
 If set (the default), sort files of equal rank in an unspecified but
 deterministic order. This makes the behaviour independent of in which