diff --git a/TESTING.md b/TESTING.md
index 4102e89..85baeac 100644
--- a/TESTING.md
+++ b/TESTING.md
@@ -87,6 +87,11 @@ with the C++ build tools. The dependency stack includes native code, so tools
 such as `cl.exe` and `lib.exe` must be available in the build environment.
 TAP-Windows6 must be installed before running the client.
 
+Use an elevated **x64 Native Tools Command Prompt for VS** or **Developer
+PowerShell for VS** for the Windows build and client run. If the commands below
+cannot find `cl`, `lib`, or `link`, install or repair Visual Studio Build Tools
+with the C++ build tools and Windows SDK, then reopen the developer shell.
+
 Quick Windows checks:
 
 ```powershell