diff --git a/FAQ.md b/FAQ.md
index bbc06c1..8cc3dc6 100644
--- a/FAQ.md
+++ b/FAQ.md
@@ -1,5 +1,8 @@
 ### Some C/C++ headers are not recognized
 
+#### Make sure company-lsp is used
+<kbd>M-x</kbd> `company-diag`, make sure`Used backend:` includes `company-lsp`. 
+
 There are at least three sets of implicit include paths. They take effect without your `-I` option in `.ccls` or `compile_commands.json`
 
 ```c++