diff --git a/completions/_cthon.zsh b/completions/_cthon.zsh
index 3e051bb..359560d 100644
--- a/completions/_cthon.zsh
+++ b/completions/_cthon.zsh
@@ -15,6 +15,7 @@ function _cthon.zsh() {
 		--srvdmesg'[print server dmesg log after running tests]' \
 		{-p,--mountpoint}'[the directory to mount the server]: : _files -/' \
 		{-r,--rdma}'[test using rdma]: :(rxe siw)' \
+		--rwsize'[test with a specific rsize & wsize]: :($(seq 4096 4096 1048576))' \
 		{-s,--server}'[the server to test against]: : _alternative
 			"hosts\:hosts\: _ssh_hosts"
 			"domains\:domains\:($(virsh list --all --name))"' \
diff --git a/cthon.zsh b/cthon.zsh
index 1170ddc..3cfcb33 100755
--- a/cthon.zsh
+++ b/cthon.zsh
@@ -13,6 +13,7 @@ zparseopts -F -K \
 	-nconnect:=NCONNECT \
 	-krb5=KRB5 \
 	r:=RDMA -rdma:=RDMA \
+	-rwsize:=RWSIZE \
 	S+=TESTS -special+=TESTS \
 	s:=SERVER -server:=SERVER \
 	x:=EXPORT -export:=EXPORT \
@@ -33,6 +34,10 @@ fi
 if [ ${#NCONNECT} -gt 0 ]; then
 	ARGS+=("--mntopt nconnect=${NCONNECT[-1]}")
 fi
+if [ ${#RWSIZE} -gt 0 ]; then
+	ARGS+=("--mntopt rsize=${RWSIZE[-1]}")
+	ARGS+=("--mntopt wsize=${RWSIZE[-1]}")
+fi
 if [ ${#KRB5} -gt 0 ]; then
 	SEC+=(krb5 krb5i krb5p)
 fi