diff --git a/README.md b/README.md
index 594285ca38..83f7b4aa88 100644
--- a/README.md
+++ b/README.md
@@ -248,7 +248,9 @@ The supported environment variables are listed in `capabilities --json`, includi
 ## Build and contribute
 
 Use the Zig version pinned in `.zig-version`, currently 0.17.0.
-On a Mac with Xcode's Metal toolchain:
+The `.metal` sources need Xcode's Metal compiler. Install full Xcode and its Metal Toolchain component
+(`xcodebuild -downloadComponent MetalToolchain`); the Command Line Tools alone fail every kernel compile with
+`unable to find utility "metal"`.
 
 ```sh
 zig build native -Dcpu=apple_m1 -Dversion=1.0.12