diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 65f5d0c..207abae 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -70,7 +70,9 @@
 
 ifeq "" "$(PLATFORM_SECURITY_PATCH)"
   # Used to indicate the security patch that has been applied to the device.
-  # Can be an arbitrary string, but must be a single word.
+  # It must signify that the build includes all security patches issued up through the designated Android Public Security Bulletin.
+  # It must be of the form "YYYY-MM-DD" on production devices.
+  # It must match one of the Android Security Patch Level strings of the Public Security Bulletins.
   #
   # If there is no $PLATFORM_SECURITY_PATCH set, keep it empty.
   PLATFORM_SECURITY_PATCH := 2016-10-05