diff --git a/source/update.js b/source/update.js
index cdafd3d5e..d85ab39b2 100644
--- a/source/update.js
+++ b/source/update.js
@@ -7,7 +7,7 @@ import always from './always.js';
  * Returns a new copy of the array with the element at the provided index
  * replaced with the given value.
  *
- * When `idx < 0 || idx >= list.length`, the original list is returned.
+ * When `idx < -list.length || idx >= list.length`, the original list is returned.
  *
  * @func
  * @memberOf R