diff --git a/Build.md b/Build.md
index ea06be0..bfd552a 100644
--- a/Build.md
+++ b/Build.md
@@ -22,14 +22,29 @@ are not supported at the moment.
 
 * `-DSYSTEM_CLANG=(ON|OFF)`
 
-  Default: ON
+  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.
 
   ```
-  % cmake -H. -Brelease -DCMAKE_INSTALL_PREFIX=/usr -DSYSTEM_CLANG=On
-  % cmake --build release
+  % cmake -H. -BRelease -DCMAKE_INSTALL_PREFIX=/usr -DSYSTEM_CLANG=On
+  % cmake --build Release
   ```
 
+  cmake will download the releases.llvm.org archive for you. If you want to download it manually:
+  ```zsh
+  rm -r Release
+  mkdir Release
+  cd Release
+  # download clang+llvm-6.0.1-x86_64-linux-gnu-ubuntu-16.04.tar.xz, verify with sha256sum and put it here
+  tar xf clang+llvm-6.0.1-x86_64-linux-gnu-ubuntu-16.04.tar.xz
+  cd ..
+  # cmake -H. -BRelease ...
+  ```
+
+* `-DCMAKE_CXX_COMPILER=/usr/bin/clang++`
+
+Build ccls with `/usr/bin/clang++`. You may use the absolute path of `Release/clang+llvm-*/bin/clang++` after clang+llvm archive is downloaded and extracted.
+
 * `-DCLANG_USE_BUNDLED_LIBC++=on`
 
   `clang+llvm*` downloaded from releases.llvm.org also provides libc++ libraries.