diff --git a/src/main/java/com/google/devtools/build/lib/actions/ArtifactRoot.java b/src/main/java/com/google/devtools/build/lib/actions/ArtifactRoot.java
index 2b65c59..d12e185 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/ArtifactRoot.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/ArtifactRoot.java
@@ -62,8 +62,8 @@
    * Constructs an ArtifactRoot given the output prefixes. (eg, "bin"), and (eg, "testlogs")
    * relative to the execRoot.
    *
-   * <p>Be careful with this method - all derived roots must be registered with the artifact factory
-   * before the analysis phase.
+   * <p>Be careful with this method - all derived roots must be within the derived artifacts tree,
+   * defined in ArtifactFactory (see {@link ArtifactFactory#isDerivedArtifact(PathFragment)}).
    */
   public static ArtifactRoot asDerivedRoot(Path execRoot, String... prefixes) {
     Path root = execRoot;