diff --git a/README.md b/README.md
index 90c59567..1bcab860 100644
--- a/README.md
+++ b/README.md
@@ -520,11 +520,11 @@ Map(3) {
To convert a Map to an Array, use [Array.from](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from). See [d3.group](#group) for examples.
-# d3.rollups(iterable, ...keys) · [Source](https://github.com/d3/d3-array/blob/main/src/group.js), [Examples](https://observablehq.com/@d3/d3-group-d3-rollup)
+# d3.rollups(iterable, reduce, ...keys) · [Source](https://github.com/d3/d3-array/blob/main/src/group.js), [Examples](https://observablehq.com/@d3/d3-group-d3-rollup)
Equivalent to [rollup](#rollup), but returns nested arrays instead of nested maps.
-# d3.flatRollup(iterable, ...keys) · [Source](https://github.com/d3/d3-array/blob/main/src/group.js), [Examples](https://observablehq.com/@d3/d3-flatgroup)
+# d3.flatRollup(iterable, reduce, ...keys) · [Source](https://github.com/d3/d3-array/blob/main/src/group.js), [Examples](https://observablehq.com/@d3/d3-flatgroup)
Equivalent to [rollup](#rollup), but returns a flat array of [*key0*, *key1*, …, *value*] instead of nested maps.