diff --git a/test/MultiDexModifiedSecondary/README.txt b/test/MultiDexModifiedSecondary/README.txt
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+MultiDexModifiedSecondary is designed to result in a multidex file that has
+the same classes.dex file as MultiDex, but a different classes2.dex.
+
+This is used in the OatFileAssistantTest.MultiDexSecondaryOutOfDate gtest.