diff --git a/llvm/docs/TestSuiteGuide.md b/llvm/docs/TestSuiteGuide.md
--- a/llvm/docs/TestSuiteGuide.md
+++ b/llvm/docs/TestSuiteGuide.md
@@ -42,6 +42,11 @@
            ../test-suite
    ```
 
+**NOTE!** if you are using your built clang, you need to have had also enabled
+`compiler-rt`, otherwise the MicroBenchmarks/XRay microbenchmarks will fail to
+compile. Make sure you add `compiler-rt` to your `LLVM_ENABLE_RUNTIMES` cmake
+flag.
+
 4. Build the benchmarks:
 
    ```text