diff --git a/lib/config/builder/value.ts b/lib/config/builder/value.ts
index cca028b..7f442be 100644
--- a/lib/config/builder/value.ts
+++ b/lib/config/builder/value.ts
@@ -145,7 +145,6 @@ export class Value<A extends ValueSpec> extends IBuilder<A> {
       name: string;
       description: string | null;
       warning: string | null;
-      selectKey: string;
       variants: Variants<{ [key: string]: { name: string; spec: InputSpec } }>;
       nullable: boolean;
       default: string | null;
diff --git a/lib/config/config-types.ts b/lib/config/config-types.ts
index ce4df9c..30b7b03 100644
--- a/lib/config/config-types.ts
+++ b/lib/config/config-types.ts
@@ -66,7 +66,6 @@ export interface ValueSpecBoolean extends WithStandalone {
 
 export interface ValueSpecUnion extends WithStandalone {
   type: "union";
-  selectKey: string;
   nullable: boolean;
   variants: Record<string, { name: string; spec: InputSpec }>;
 }
@@ -161,3 +160,5 @@ export type UniqueBy =
   | { all: readonly UniqueBy[] | UniqueBy[] };
 
 export type DefaultString = string | { charset: string; len: number };
+
+export const unionSelectKey = 'unionSelectKey' as const
diff --git a/scripts/oldSpecToBuilder.ts b/scripts/oldSpecToBuilder.ts
index b6f1398..258150d 100644
--- a/scripts/oldSpecToBuilder.ts
+++ b/scripts/oldSpecToBuilder.ts
@@ -143,7 +143,6 @@ export default async function makeFileContent(
         name: ${JSON.stringify(value.name || null)},
         description: ${JSON.stringify(value.tag.description || null)},
         warning: ${JSON.stringify(value.tag.warning || null)},
-        selectKey: ${JSON.stringify(value.tag.id || null)},
         nullable: false,
         default: ${JSON.stringify(value.default || null)},
         variants: ${variants},
@@ -267,9 +266,6 @@ export default async function makeFileContent(
                 warning: ${JSON.stringify(
                   value?.spec?.tag?.warning || null
                 )},
-                selectKey: ${JSON.stringify(
-                  value?.spec?.tag?.id || null
-                )},
                 variants: ${variants},
                 nullable: false,
               }