diff --git a/Build.md b/Build.md
index aca3830..908a5e8 100644
--- a/Build.md
+++ b/Build.md
@@ -18,7 +18,7 @@ You may append `-G Ninja -DCMAKE_CXX_LINK_FLAGS=-fuse-ld=lld -DCMAKE_CXX_COMPILE
 * `-DSYSTEM_CLANG=(ON|OFF)`
 
   Default: OFF
-  Enable `SYSTEM_CLANG` if you want to link ccls against a system/local Clang instead of downloading Clang from releases.llvm.org during the configure process.
+  Enable `SYSTEM_CLANG` if you want to link ccls against a system/local Clang instead of downloading Clang from releases.llvm.org during the configure process. You will probably need to install libclang-*-dev and llvm-*-dev packages (or equivalent) in order to have the correct libraries.
 
   ```zsh
   % cmake -H. -BRelease -DCMAKE_INSTALL_PREFIX=/usr -DSYSTEM_CLANG=On