diff --git a/README.md b/README.md
index a644d389..41a28cda 100644
--- a/README.md
+++ b/README.md
@@ -149,7 +149,7 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 - [util/sort](https://openhome.cc/eGossip/OpenSCAD/lib3x-sort.html)
 - [util/sub_str](https://openhome.cc/eGossip/OpenSCAD/lib3x-sub_str.html)
 - [util/split_str](https://openhome.cc/eGossip/OpenSCAD/lib3x-split_str.html)
-- [util/sum](https://openhome.cc/eGossip/OpenSCAD/lib2x-sum.html)
+- [util/sum](https://openhome.cc/eGossip/OpenSCAD/lib3x-sum.html)
 - [util/zip](https://openhome.cc/eGossip/OpenSCAD/lib2x-zip.html)
 
 ### Matrix
diff --git a/docs/lib2x-sum.md b/docs/lib3x-sum.md
similarity index 100%
rename from docs/lib2x-sum.md
rename to docs/lib3x-sum.md
diff --git a/src/util/sum.scad b/src/util/sum.scad
index c2e5c1be..762afe92 100644
--- a/src/util/sum.scad
+++ b/src/util/sum.scad
@@ -4,7 +4,7 @@
 * @copyright Justin Lin, 2020
 * @license https://opensource.org/licenses/lgpl-3.0.html
 *
-* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-sum.html
+* @see https://openhome.cc/eGossip/OpenSCAD/lib3x-sum.html
 *
 **/