diff --git a/docs/contributing/how-to-write-unit-tests.md b/docs/contributing/how-to-write-unit-tests.md
index 77563a0c89..b419914cf2 100644
--- a/docs/contributing/how-to-write-unit-tests.md
+++ b/docs/contributing/how-to-write-unit-tests.md
@@ -27,6 +27,10 @@ build the library:
   directory where you ran configure, not the one in the source tree) and run
   `make test` (non-GUI tests) or `make test_gui` (GUI ones) to build.
 
+- When using CMake, add `-DwxBUILD_TESTS=ON` (or `=CONSOLE` for non-GUI tests
+  only) to the command line arguments, or choose the desired `wxBUILD_TESTS`
+  option in `cmake-gui`.
+
 - When using `makefile.vc` or `makefile.gcc` under MSW to build the libraries,
   use the same makefile under `tests` to build the tests.