diff --git a/tools/fs_config/default/android_filesystem_config.h b/tools/fs_config/default/android_filesystem_config.h
index b7d936a..820b04a 100644
--- a/tools/fs_config/default/android_filesystem_config.h
+++ b/tools/fs_config/default/android_filesystem_config.h
@@ -19,6 +19,13 @@
 ** by the device side of adb.
 */
 
+/*
+** Resorting to the default file means someone requested fs_config_dirs or
+** fs_config_files in their device configuration without providing an
+** associated header.
+*/
+#warning No device-supplied android_filesystem_config.h, using empty default.
+
 /* Rules for directories.
 ** These rules are applied based on "first match", so they
 ** should start with the most specific path and work their