diff --git a/compat/README b/compat/README
index 38e2e146..12aacf42 100644
--- a/compat/README
+++ b/compat/README
@@ -1,6 +1,6 @@
 notmuch/compat
 
-This directory consists of two things:
+This directory consists of three things:
 
 1. Small programs used by the notmuch configure script to test for the
    availability of certain system features, (library functions, etc.).
@@ -14,3 +14,8 @@ This directory consists of two things:
 
    The compilation of these files is made conditional on the output of
    the test programs from [1].
+
+3. Macro definitions abstracting compiler differences (e.g. function
+   attributes).
+
+   For example: function-attributes.h