diff --git a/Build.md b/Build.md
index 5c3a5fc..e3e54bc 100644
--- a/Build.md
+++ b/Build.md
@@ -132,7 +132,10 @@ To install pre-built **ccls**, use
 [aur/ccls-git](https://aur.archlinux.org/packages/ccls-git).
 
 To build **ccls** on Arch Linux with system Clang+LLVM, you will need to add
-`-DLLVM_ENABLE_RTTI=on`.
+`-DLLVM_ENABLE_RTTI=on -DUSE_SHARED_LLVM=on`.
+
+`extra/clang` and `extra/llvm` provide `/usr/lib/{libclangAST.so,libLLVM*.a,libLLVM.so}`.
+`libclangAST.so` needs `libLLVM.so` and there would be a conflict if `libLLVM*.a` (instead of `libLLVM.so`) are linked. See https://bugs.archlinux.org/task/60512
 
 ### Gentoo Linux