diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/AutoValueSubclassLeaked.java b/core/src/main/java/com/google/errorprone/bugpatterns/AutoValueSubclassLeaked.java
index <HASH>..<HASH> 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/AutoValueSubclassLeaked.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/AutoValueSubclassLeaked.java
@@ -48,7 +48,13 @@ import com.sun.tools.javac.code.Type;
     severity = WARNING,
     summary =
         "Do not refer to the autogenerated AutoValue_ class outside the file containing the"
-            + " corresponding @AutoValue base class.")
+            + " corresponding @AutoValue base class.",
+    explanation =
+        "@AutoValue-annotated classes may form part of your API, but the AutoValue_ generated"
+            + " classes should not. The fact that the generated classes are visible to other"
+            + " classes within the same package is an implementation detail, and is best avoided."
+            + " Ideally, any reference to the AutoValue_-prefixed class sould be confined to a"
+            + " single factory method, with other factories delegating to it if necessary.")
 public final class AutoValueSubclassLeaked extends BugChecker
     implements CompilationUnitTreeMatcher {
AutoValueSubclassLeaked: point it at the AutoValue FAQ.

Add a problem statement for open source world.

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