diff --git a/llvm/docs/TestSuiteGuide.md b/llvm/docs/TestSuiteGuide.md
index 699f9adc39d77d..296b34a3273768 100644
--- a/llvm/docs/TestSuiteGuide.md
+++ b/llvm/docs/TestSuiteGuide.md
@@ -42,6 +42,10 @@ Quickstart
            ../test-suite
    ```
 
+**NOTE!** if you are using your built clang, and you want to build and run the
+MicroBenchmarks/XRay microbenchmarks, you need to add `compiler-rt` to your
+`LLVM_ENABLE_RUNTIMES` cmake flag.
+
 4. Build the benchmarks:
 
    ```text