diff --git a/test/readme.md b/test/readme.md
index b74364ff..db3524cd 100644
--- a/test/readme.md
+++ b/test/readme.md
@@ -1,7 +1,7 @@
 Testing allocators is difficult as bugs may only surface after particular
 allocation patterns. The main approach to testing _mimalloc_ is therefore
 to have extensive internal invariant checking (see `page_is_valid` in `page.c`
-for example), which is enabled in debug mode with `-DMI_CHECK_FULL=ON`.
+for example), which is enabled in debug mode with `-DMI_DEBUG_FULL=ON`.
 The main testing strategy is then to run [`mimalloc-bench`][bench] using full
 invariant checking to catch any potential problems over a wide range of intensive
 allocation benchmarks and programs.