diff --git a/README.md b/README.md
index 2cce93799e6921c71731806a33bca8c6bcdccfec..7e605c51e7a18ab2a96a2a150e2a5d7ad904b5c7 100644
--- a/README.md
+++ b/README.md
@@ -123,6 +123,9 @@ To run a specific individual test, use the `gpos_test` executable directly.
 ./server/gpos_test -U CAutoTaskProxyTest
 ```
 
+Note that some tests use assertions that are only enabled for DEBUG builds, so
+DEBUG-mode tests tend to be more rigorous.
+
 ### Advanced: Extended Tests
 
 Debug builds of GPOS include a couple of "extended" tests for features like