diff --git a/require-ess/tools/driver.makefile b/require-ess/tools/driver.makefile
index 8c5b889c55df260f3204ece3f2494d7ad0ecac43..ed99c3cbeade7585556b741d3f466462fe8888b2 100644
--- a/require-ess/tools/driver.makefile
+++ b/require-ess/tools/driver.makefile
@@ -188,6 +188,9 @@ ${CONFIG}/CONFIG:
 # Variables that need to override data from ${CONFIG}/CONFIG
 BASE_CPPFLAGS=
 
+# This is (at the moment) only used for a single module. If LEGACY_RSET is defined then
+# we use the _old_ untyped `struct rset` definitions for record device support. Otherwise,
+# we use the updated `struct typed_rset` ones. This helps remove some compiler warnings.
 ifndef LEGACY_RSET
 USR_CPPFLAGS+=-DUSE_TYPED_RSET
 endif