diff --git a/llvm/docs/TestSuiteGuide.md b/llvm/docs/TestSuiteGuide.md
--- a/llvm/docs/TestSuiteGuide.md
+++ b/llvm/docs/TestSuiteGuide.md
@@ -42,6 +42,10 @@
            ../test-suite
    ```
 
+**NOTE!** if you are using your built clang, you need to have had also enabled
+`compiler-rt`, otherwise the XRay microbenchmarks will fail to compile. Make
+sure you add `compiler-rt` to your `LLVM_ENABLE_PROJECTS` cmake flag.
+
 4. Build the benchmarks:
 
    ```text