diff --git a/Changes.md b/Changes.md
index 2d5cd9766d..1ed6bf81d1 100644
--- a/Changes.md
+++ b/Changes.md
@@ -1,5 +1,15 @@
 # Build System Changes for Android.mk Writers
 
+## `USER` deprecation  {#USER}
+
+`USER` will soon be `nobody` in many cases due to the addition of a sandbox
+around the Android build. Most of the time you shouldn't need to know the
+identity of the user running the build, but if you do, it's available in the
+make variable `BUILD_USERNAME` for now.
+
+Similarly, the `hostname` tool will also be returning a more consistent value
+of `android-build`. The real value is available as `BUILD_HOSTNAME`.
+
 ## `BUILD_NUMBER` removal from Android.mk  {#BUILD_NUMBER}
 
 `BUILD_NUMBER` should not be used directly in Android.mk files, as it would
diff --git a/core/config.mk b/core/config.mk
index 59b8de00bc..18f844d1fb 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -90,6 +90,7 @@ $(KATI_obsolete_var \
   GLOBAL_CFLAGS_NO_OVERRIDE GLOBAL_CPPFLAGS_NO_OVERRIDE \
   ,GCC support has been removed. Use Clang instead)
 $(KATI_obsolete_var DIST_DIR dist_goal,Use dist-for-goals instead. See $(CHANGES_URL)#dist)
+$(KATI_deprecated_var USER,Use BUILD_USERNAME instead. See $(CHANGES_URL)#USER)
 
 # This is marked as obsolete in envsetup.mk after reading the BoardConfig.mk
 $(KATI_deprecate_export It is a global setting. See $(CHANGES_URL)#export_keyword)