diff --git a/draftlogs/8128_fix.md b/draftlogs/8128_fix.md
new file mode 100644
index 00000000000..074a5f73357
--- /dev/null
+++ b/draftlogs/8128_fix.md
@@ -0,0 +1 @@
+- Fix `ternary.sum` relayout to recalculate ternary trace data [[#8128](https://github.com/plotly/plotly.js/pull/8128)]
diff --git a/src/plots/ternary/layout_attributes.js b/src/plots/ternary/layout_attributes.js
index 752837ca92b..363e6851714 100644
--- a/src/plots/ternary/layout_attributes.js
+++ b/src/plots/ternary/layout_attributes.js
@@ -98,6 +98,9 @@ var attrs = module.exports = overrideAll({
     caxis: ternaryAxesAttrs
 }, 'plot', 'from-root');
 
+// ternary.sum is used by calc to normalize
+attrs.sum.editType = 'calc';
+
 // set uirevisions outside of `overrideAll` so we can get `editType: none`
 attrs.uirevision = {
     valType: 'any',
diff --git a/test/plot-schema.json b/test/plot-schema.json
index 4d51312e82d..2783212ffbc 100644
--- a/test/plot-schema.json
+++ b/test/plot-schema.json
@@ -12427,7 +12427,7 @@
         "sum": {
           "description": "The number each triplet should sum to, and the maximum range of each axis",
           "dflt": 1,
-          "editType": "plot",
+          "editType": "calc",
           "min": 0,
           "valType": "number"
         },