diff --git a/libcutils/include/private/android_filesystem_config.h b/libcutils/include/private/android_filesystem_config.h
index bdb807538..da5005cd5 100644
--- a/libcutils/include/private/android_filesystem_config.h
+++ b/libcutils/include/private/android_filesystem_config.h
@@ -41,9 +41,11 @@
  */
 
 #define AID_ROOT 0 /* traditional unix root user */
-/* The following are for LTP and should only be used for testing */
-#define AID_DAEMON 1 /* traditional unix daemon owner */
-#define AID_BIN 2    /* traditional unix binaries owner */
+
+/* The following are for tests like LTP and should only be used for testing. */
+#define AID_DAEMON 1 /* Traditional unix daemon owner. */
+#define AID_BIN 2    /* Traditional unix binaries owner. */
+#define AID_SYS 3    /* A group with the same gid on Linux/macOS/Android. */
 
 #define AID_SYSTEM 1000 /* system server */