diff --git a/Build.md b/Build.md
index 7a3ba72..e14f04c 100644
--- a/Build.md
+++ b/Build.md
@@ -160,7 +160,8 @@ sudo zypper install ccls
 
 ### Ubuntu
 
-To build from source you'll need `sudo apt install zlib1g-dev libncurses-dev`
+To build from source you'll need `sudo apt install zlib1g-dev libncurses-dev`.
+To use system rapidjson, install `rapidjson-dev`.
 
 On Ubuntu 16.04 install g++-7 via [these directions](https://gist.github.com/jlblancoc/99521194aba975286c80f93e47966dc5)