diff --git a/packages/frontend-core/src/components/grid/stores/columns.ts b/packages/frontend-core/src/components/grid/stores/columns.ts
index d67b0dd8e8..8073988323 100644
--- a/packages/frontend-core/src/components/grid/stores/columns.ts
+++ b/packages/frontend-core/src/components/grid/stores/columns.ts
@@ -190,6 +190,7 @@ export const initialise = (context: StoreContext) => {
             related: fieldSchema.related,
             calculationType: fieldSchema.calculationType,
             __left: undefined as any, // TODO
+            __idx: undefined as any, // TODO
           }
           // Override a few properties for primary display
           if (field === primaryDisplay) {
diff --git a/packages/types/src/ui/stores/grid/columns.ts b/packages/types/src/ui/stores/grid/columns.ts
index 56442a871f..7f20145246 100644
--- a/packages/types/src/ui/stores/grid/columns.ts
+++ b/packages/types/src/ui/stores/grid/columns.ts
@@ -16,7 +16,7 @@ export type UIColumn = FieldSchema & {
     autocolumn: boolean
   }
   calculationType: CalculationType
-  __idx?: number
+  __idx: number
   __left: number
   width: number
 }