diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index c23ee58..8009f00 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -24,3 +24,6 @@ uv run --with cmake --with ninja cmake --preset host -DPython3_EXECUTABLE=/usr/b
 
 Pass `-DPython3_EXECUTABLE=/usr/bin/python3` explicitly — without it the fixture step
 captures uv's ephemeral interpreter, which disappears after the run.
+
+Two lanes independently hit the CMake floor, so to be explicit: if you do not want to build on
+CT111, `uv tool install cmake` puts a current CMake on `~/.local/bin` and works for the host preset.