diff --git a/docs/revsets.md b/docs/revsets.md
index 1d78f1b2fa..c48740d8be 100644
--- a/docs/revsets.md
+++ b/docs/revsets.md
@@ -79,7 +79,8 @@ revsets (expressions) as arguments.
 
 * `parents(x)`: Same as `x-`.
 * `children(x)`: Same as `x+`.
-* `ancestors(x)`: Same as `:x`.
+* `ancestors(x[, depth])`: Last `depth` ancestors of `x` (including `x` 
+  itself). `ancestors(x)` is the same as `:x`, returning all ancestors.
 * `descendants(x)`: Same as `x:`.
 * `connected(x)`: Same as `x:x`. Useful when `x` includes several commits.
 * `all()`: All visible commits in the repo.