diff --git a/demo/Readme.md b/demo/Readme.md
index 514d2d8..8efe7aa 100644
--- a/demo/Readme.md
+++ b/demo/Readme.md
@@ -28,6 +28,7 @@ sudo make install
 sudo apt-get install autoconf automake autotools-dev curl libmpc-dev libmpfr-dev libgmp-dev libusb-1.0-0-dev gawk build-essential bison flex texinfo gperf libtool patchutils bc zlib1g-dev device-tree-compiler pkg-config libexpat-dev libfl-dev
 git clone https://github.com/chipsalliance/rocket-tools.git
 git submodule update --init --recursive
+# riscv-isa-sim and openocd may be checkout to main branch to avoid compile error
 sudo su
 export RISCV=/opt/riscv
 export MAKEFLAGS="-j12"