diff --git a/Makefile b/Makefile
index 017fc65..2ec988e 100644
--- a/Makefile
+++ b/Makefile
@@ -735,6 +735,9 @@
     endif
 endif
 
+# Trusted Boot is a prerequisite for Measured Boot. It provides trust that the
+# code taking the measurements and recording them has not been tampered
+# with. This is referred to as the Root of Trust for Measurement.
 ifeq ($(MEASURED_BOOT),1)
     ifneq (${TRUSTED_BOARD_BOOT},1)
         $(error MEASURED_BOOT requires TRUSTED_BOARD_BOOT=1)