diff --git a/src/main/java/com/android/tools/metalava/Options.kt b/src/main/java/com/android/tools/metalava/Options.kt
index 9e81d24..8c91b18 100644
--- a/src/main/java/com/android/tools/metalava/Options.kt
+++ b/src/main/java/com/android/tools/metalava/Options.kt
@@ -76,6 +76,9 @@
 const val ARG_KOTLIN_STUBS = "--kotlin-stubs"
 const val ARG_STUBS_SOURCE_LIST = "--write-stubs-source-list"
 const val ARG_DOC_STUBS_SOURCE_LIST = "--write-doc-stubs-source-list"
+/**
+ * Used by Firebase, see b/116185431#comment15, not used by Android Platform or AndroidX
+ */
 const val ARG_PROGUARD = "--proguard"
 const val ARG_EXTRACT_ANNOTATIONS = "--extract-annotations"
 const val ARG_EXCLUDE_ALL_ANNOTATIONS = "--exclude-all-annotations"